Fix reversing 1bpp images

Fixes #2075

src/gfx/reverse.cpp

@@ -569,7 +569,7 @@ void reverse() {
 				// If vertically mirrored, fetch the bytes from the other end
 				uint8_t realY = (attribute & 0x40 ? 7 - y : y) * options.bitDepth;
 				uint8_t bitplane0 = tileData[realY];
-				uint8_t bitplane1 = options.bitDepth == 2 ? tileData[realY + 1] : bitplane0;
+				uint8_t bitplane1 = options.bitDepth == 2 ? tileData[realY + 1] : 0;
 				if (attribute & 0x20) { // Handle horizontal flip
 					bitplane0 = flipTable[bitplane0];
 					bitplane1 = flipTable[bitplane1];

test/gfx/reverse_1bit_palette.1bpp

@@ -0,0 +1 @@
+

test/gfx/reverse_1bit_palette.flags

@@ -0,0 +1 @@
+-p reverse_1bit_palette.pal