fix: potential wrap in RGB API - #129

==19382==ERROR: AddressSanitizer: BUS on unknown address (pc 0x00018b6cd520 bp 0x00016d85ba70 sp 0x00016d85b220 T0)
==19382==The signal is caused by a WRITE memory access.
==19382==Hint: this fault was caused by a dereference of a high value address (see register values below).  Disassemble the provided pc to learn which register was used.
    #0 0x00018b6cd520 in _platform_memmove+0x1c0 (libsystem_platform.dylib:arm64e+0x3520)
    #1 0x0001025a93d0 in crawl_decision_tree+0x7a4 (a.out:arm64+0x1000093d0)
    #2 0x0001025a6774 in create_decision_tree+0x180 (a.out:arm64+0x100006774)
    #3 0x0001025a3f10 in quantize_and_dither+0x1d4 (a.out:arm64+0x100003f10)
    #4 0x0001025a2e34 in cgif_rgb_addframe+0xdfc (a.out:arm64+0x100002e34)
    #5 0x0001025a0cec in main+0x50c (a.out:arm64+0x100000cec)
    #6 0x00018b2f84e0 in start+0x1b4c (dyld:arm64e+0x204e0)