arb_texture_view: test for NaN in more cases
When the image has a float format, the test shader will be using float texelFetch to test it. When we're clearing the image with a NaN bit pattern, this becomes a problem as some hardware like ARM Mali does not preserve NaN sign bit (or possibly the entire bit pattern) so a texel that had 0x7fffffff written into it comes up as 0xffffffff.
Make the test take a test_nan path in cases when NaN bit pattern will be written into a float-typed image as NaN propagation details should not affect the outcome of the test.