[ttgxvar] Avoid "applying zero offset to null pointer"
In C it is undefined behavior to do arithmetic on a null pointer, including
adding zero. When using NotoSansKhmer[wdth,wght].ttf UBSAN produces a report
like
ttgxvar.c:1052:31: runtime error: applying zero offset to null pointer
when adding zero to `varData->deltaSet` (which is null) to produce `bytes`.
Protect against all the potential issues of this kind by returning early if
`varData->regionIdxCount == 0`.
* src/truetype/ttgxvar.c (tt_var_get_item_delta): early return on no regions
diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c
index 7d67d5f..095a720 100644
--- a/src/truetype/ttgxvar.c
+++ b/src/truetype/ttgxvar.c
@@ -1028,6 +1028,9 @@
if ( innerIndex >= varData->itemCount )
return 0; /* Out of range. */
+ if ( varData->regionIdxCount == 0 )
+ return 0; /* Avoid "applying zero offset to null pointer". */
+
if ( varData->regionIdxCount < 16 )
{
deltaSet = deltaSetStack;
