Fixed segfault in AbstractTexture::bind().

Caused in 6ee2745503, I accidentaly
removed code that initialized the array to proper length. Again I
experienced how useful unit tests for GL functionality would be.

src/AbstractTexture.cpp

@@ -233,6 +233,9 @@ void AbstractTexture::bindInternal() {
 }
 
 void AbstractTexture::initializeContextBasedFunctionality(Context& context) {
+    /* Resize bindings array to hold all possible layers */
+    context.state().texture->bindings.resize(maxLayers());
+
     #ifndef MAGNUM_TARGET_GLES
     if(context.isExtensionSupported<Extensions::GL::EXT::direct_state_access>()) {
         Debug() << "AbstractTexture: using" << Extensions::GL::EXT::direct_state_access::string() << "features";