fix: Prevent NULL pointer dereference in DVB subtitle decoder

[cfsmp3]

Summary

• Add NULL check for region before accessing region->bgcolor in the OCR processing block of write_dvb_sub()

Problem

When processing DVB subtitles, the write_dvb_sub() function iterates through display items calling get_region(). After the loop, if all regions returned NULL, the region variable remains NULL. The code then attempts to access region->bgcolor in the OCR block, causing a segmentation fault.

Crash details:

• Valgrind: "Invalid read of size 4 at address 0x18"
• The 0x18 offset (24 bytes) corresponds to the bgcolor field in DVBSubRegion struct

Root Cause

for (display = ctx->display_list; display; display = display->next)
{
    region = get_region(ctx, display->region_id);
    if (!region)
        continue;  // region is still NULL here
    // ...
}
// After loop: region may be NULL

if (ctx->ocr_ctx)  // Missing check for region != NULL
{
    int ret = ocr_rect(..., region->bgcolor, ...);  // CRASH if region is NULL
}

Fix

Add && region to the condition before the OCR block.

Test Plan

• Build completes successfully
• bbc_small.ts: Before fix = SIGSEGV crash, After fix = 100% processed, 50+ subtitles extracted
• No regressions expected - the change only adds a NULL guard

🤖 Generated with Claude Code

[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 2f29040...:

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
• ccextractor --out=spupng c83f765c66..., 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 d837c36...:

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	81/86
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 --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 --out=spupng c83f765c66..., 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.