fix: add NULL pointer check in scanner.c (CWE-476)

[anupamme]

Multiple malloc calls in src/scanner.c do not check for NULL return values before dereferencing the allocated pointer. At line 19, malloc(sizeof(LexerState)) is not checked before accessing state->start_tag. At line 35, malloc result is assigned to text and immediately used. At line 42, malloc result is assigned to tmp and used. At line 56, malloc result is assigned to text_size and used. Under memory pressure, these allocations can fail and return NULL, causing immediate segmentation fault when dereferenced. The affected code is src/scanner.c:18, and this change addresses it.

Reference: CWE-476

What changed

• src/scanner.c

Verification

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