Fix palette indexing bug

src/f6502.c

@@ -228,7 +228,7 @@ static inline int f6502_write(nes_Memory* mem,
                             pal[16] = pal[20] = pal[24] =
                             pal[28] = 0xFFU;
                     } else {
-                        pal[addr] = val;
+                        pal[addr] = val & 0x3FU;
                     }
 
                     // Memory-mapped mirroring

src/nes.c

@@ -87,8 +87,9 @@ static int nes_hsync(nes* sys, void* plat) {
         // Emulate the happy part of the backdrop override quirk
         int pal_idx = ((mem->addr & 0x3F00U) == 0x3F00U) ?
                       (mem->addr & 0x1FU) : 0;
+        LOGD("Background: %d", pal_idx);
         // Don't use the rendering palette (masked transparency)
-        status = nese_frame_start(plat, mem->pal_bank[0x300 + pal_idx]);
+        status = nese_frame_start(plat, mem->pal_bank[0x300 + pal_idx] & 0x3FU);
 
     }   break;