CVE-2026-71266: tinyobjloader-c Stack Buffer Overflow in MTL Material File Line Parsing

tinyobjloader-c's tinyobjparseandindexmtlfile() (tinyobjloaderc.h) reads each line of a .mtl material file into a fixed 4096-byte stack buffer linebuf via memcpy(linebuf, p, plen), guarded only by assert(plen < 4095). Because assert() compiles to a no-op under -DNDEBUG (standard for release builds), a crafted .mtl file containing a line (e.g. a "newmtl" material name) longer than 4096 bytes overflows linebuf into the adjacent stack variable namebuf and beyond, corrupting the stack of any application that loads attacker-supplied 3D model/material files. The identical vulnerable pattern is duplicated in a second function in the same file.