[sixel] don't use more than 65534 color registers

src/lib/sprite.h

@@ -9,6 +9,8 @@ extern "C" {
 #include <stdbool.h>
 #include "fbuf.h"
 
+#define SIXEL_MAX_REGISTERS 65534 // 65535 is used for transparent
+
 struct tinfo;
 struct ncpile;
 struct ncplane;

src/lib/termdesc.c

@@ -1215,7 +1215,9 @@ handle_responses(tinfo* ti, size_t* tablelen, size_t* tableused,
   }
   // kitty trumps sixel, when both are available
   if((*kitty_graphics = iresp->kitty_graphics) == 0){
-    ti->color_registers = iresp->color_registers;
+    if((ti->color_registers = iresp->color_registers) > SIXEL_MAX_REGISTERS){
+      ti->color_registers = SIXEL_MAX_REGISTERS;
+    }
     ti->sixel_maxy_pristine = iresp->sixely;
     ti->sixel_maxy = iresp->sixely;
     ti->sixel_maxx = iresp->sixelx;