Fix CHR_ROM size overflow

src/ppu.h

@@ -103,11 +103,11 @@ typedef struct {
     uint16_t t;         // temp VRAM addr
     uint8_t latch;      // aka "w" - TODO: Could this be a flag?
     uint8_t addr_inc;   // Auto-increment (1 or 32)
-    uint8_t unused[2];  // 2 B unused
     uint8_t bus;        // Last value transmitted (NOT next data val)
+    uint8_t unused; // NOTE: 1 B unused
 
     // Static memory banks
-    uint8_t n_chr_banks; // TODO: Changed from int; consequences?
+    int16_t n_chr_banks; // TODO: Changed from int; consequences?
     uint8_t palette[32]; // Rendering palette with transparency masked
     uint8_t pal_ram[32]; // Raw palette data in RAM
     uint8_t oam[NES_PPU_OAM_SIZE];