Specify layout index in shader

shaders/image.frag

@@ -7,7 +7,7 @@ uniform bool invert;
 uniform bool srgb;
 uniform vec3 whiteBalance;
 in vec2 qt_TexCoord0;
-out vec4 color;
+layout(location = 0) out vec4 color;
 
 vec3 Linear2sRGB(vec3 color)
 {