[3.x] Fix incompatible addition in auto exposure shader

[timothyqiu]

After turning on auto exposure on my Android device, it produces a shader compilation error:

E 0:00:02.057   _display_error_with_code: ExposureShaderGLES3: Fragment Program Compilation Failed:
ERROR: 0:38: '+' :  wrong operand types  no operation '+' exists that takes a left-hand operand of type '2-component vector of float' and a right operand of type 'const 2-component vector of int' (or there is no acceptable conversion)
ERROR: 1 compilation errors.  No code generated.

It complains about gl_FragCoord.xy + ivec2(1) operands being incompatible, and auto exposure fails to work even if I change framebuffer allocation type to 3D.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.4.1.