Add many checks to protect against malformed PCF files.

* src/pcf/pcfdrivr.c (PCF_Face_Done): Protect against NULL pointers.
(PCF_Face_Init): Add calls to PCF_Face_Done in case of errors.

* src/pcf/pcfread.c (pcf_read_TOC): Protect against malformed table
data and check that tables don't overlap (using a simple
bubblesort).
(PCF_METRIC_SIZE, PCF_COMPRESSED_METRIC_SIZE, PCF_PROPERTY_SIZE):
New macros which give the size of data structures in the data
stream.
(pcf_get_properties): Use rough estimates to get array size limits.
Assign `face->nprops' and `face->properties' earlier so that a call
to PCF_Face_Done can do the clean-up in case of error.
Protect against invalid string offsets.
(pcf_get_metrics): Clean up code.
Adjust tracing message levels.
Use rough estimate to get array size limit.
(pcf_get_bitmaps): Clean up code.
Adjust tracing message levels.
Use rough estimates to get offset limits.
(pcf_get_encodings): Adjust tracing message level.
(pcf_get_accel): Clean up code.
3 files changed