QOpenGLShaderProgram: glProgramBinary() resulting in LINK_STATUS=FALSE not handled properly

Reported in freedesktop.org bug: https://bugs.freedesktop.org/show_bug.cgi?id=105065

When glProgramBinary() results in LINK_STATUS = FALSE, this path through the code causes an empty program to be linked instead of with the provided shaders:
1) qopenglshaderprogram.cpp:3825: if (binCache.load(cacheKey, q->programId())) {

does glProgramBinary(). Mesa doesn't like the binary and sets the link
status to failure.

2) qopenglshaderprogram.cpp:3825: bool ok = q->link();

To check link status

3) qopenglshaderprogram.cpp:1297: d->glfuncs->glGetProgramiv(program, GL_LINK_STATUS, &value);

Sees that glProgramBinary set link status to failed.

4) qopenglshaderprogram.cpp:1303: d->glfuncs->glLinkProgram(program);

Links the program, however no shaders have been attached. Because a
compat context is being used, this is valid and linking succeeds.

5) qopenglshaderprogram.cpp:1324: return d->linked;

returns true;

6) qopenglshaderprogram.cpp:3831: needsCompile = false;

Won't try to compile, have a program with no shaders at this point.