Uniform location lookups inside QSGSimpleMaterialShader::resolveUniforms fails sometimes

When looking up uniform locations inside the resolveUniforms-function in a QSGSimpleMaterialShader-based class, some of them will not be found.

In particular, when having multiple sampler2D-uniforms in the fragment shader, only the first one will be found. Locations for the other ones are reported as -1.

However, if calling "program()->bind()" first, everything works as expected.

After a discussion with Mr. Sletta on IRC, I recommend adding this "program()->bind()"-call at the end of QSGMaterialShader::initialize(). This way the program will be bound before resolveUniforms is called.

I have reproduced the issue both on a Desktop nvidia card, as well as an embedded arm device with a SGX530-gpu.