fix DTVCC: Structural type confusion / OOB writes

[THE-Amrit-mahto-05]

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Title: [FIX] DTVCC: Structural type confusion / OOB writes (#1961)

Description:
This PR addresses a critical structural type confusion and out-of-bounds (OOB) write in the DTVCC (CEA-708) decoder.

Issue: #1961

Problem:
Malformed or malicious CEA-708 streams could define windows with row/column counts exceeding the maximums. This could lead to:

• Heap buffer over-reads
• Reading struct members as pointers (information leak)
• Overwriting TV screen metadata
• Undefined behavior during caption extraction

Fix implemented:

• Added bounds checks for row_count and col_count in dtvcc_handle_DFx_DefineWindow.
• Added safety checks for pen_row and pen_column in dtvcc_process_character and dtvcc_handle_SPL_SetPenLocation.
• Added invariant check in dtvcc_window_copy_to_screen to reject windows exceeding maximum dimensions.
• Logging added for invalid dimensions and pen positions for easier debugging.

Impact:

• Prevents out-of-bounds memory access.
• Ensures decoder robustness against malformed streams.

Testing:

• Verified windows exceeding CCX_DTVCC_MAX_ROWS/COLUMNS are rejected.
• Verified pen positions outside valid bounds are ignored safely.
• Confirmed normal streams continue to work correctly with no regression.

[ccextractor-bot]

CCExtractor CI platform finished running the test files on linux. Below is a summary of the test results, when compared to test for commit a5b8bc8...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	25/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	81/86
Teletext	21/21
WTV	13/13
XDS	34/34

Your PR breaks these cases:

• ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65...
• ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b...
• ccextractor --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotbefore 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotafter 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatleast 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatmost 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...

Congratulations: Merging this PR would fix the following tests:

• ccextractor --autoprogram --out=srt --latin1 --quant 0 85271be4d2..., Last passed: Never

It seems that not all tests were passed completely. This is an indication that the output of some files is not as expected (but might be according to you).

Check the result page for more info.

[ccextractor-bot]

CCExtractor CI platform finished running the test files on windows. Below is a summary of the test results, when compared to test for commit a5b8bc8...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	6/7
DVD	3/3
DVR-MS	2/2
General	25/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	80/86
Teletext	21/21
WTV	13/13
XDS	34/34

Your PR breaks these cases:

• ccextractor --autoprogram --out=srt --latin1 --quant 0 85271be4d2...
• ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65...
• ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b...
• ccextractor --out=spupng c83f765c66...
• ccextractor --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotbefore 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotafter 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatleast 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatmost 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...

It seems that not all tests were passed completely. This is an indication that the output of some files is not as expected (but might be according to you).

Check the result page for more info.

[cfsmp3]

Closing - all commits are included in #1968.