GPU: Fix unhandled R16G16_UNORM in SDL_GPUTextureFormatTexelBlockSize() (#10638)

src/gpu/SDL_gpu.c

@@ -532,6 +532,7 @@ Uint32 SDL_GPUTextureFormatTexelBlockSize(
     case SDL_GPU_TEXTUREFORMAT_R10G10B10A2_UNORM:
     case SDL_GPU_TEXTUREFORMAT_R8G8B8A8_UINT:
     case SDL_GPU_TEXTUREFORMAT_R16G16_UINT:
+    case SDL_GPU_TEXTUREFORMAT_R16G16_UNORM:
         return 4;
     case SDL_GPU_TEXTUREFORMAT_R16G16B16A16_FLOAT:
     case SDL_GPU_TEXTUREFORMAT_R16G16B16A16_UNORM: