Properly initialize variables for texture limits in state tracker.

And I was wondering how it is possible that there new NVidia drivers
were allowing up to 32 PB textures on my humble laptop graphics :)

src/Magnum/Implementation/TextureState.cpp

@@ -36,7 +36,11 @@
 
 namespace Magnum { namespace Implementation {
 
-TextureState::TextureState(Context& context, std::vector<std::string>& extensions): maxTextureUnits(0), maxLodBias(0.0f), maxMaxAnisotropy(0.0f), currentTextureUnit(0)
+TextureState::TextureState(Context& context, std::vector<std::string>& extensions): maxSize{}, max3DSize{}, maxArrayLayers{}, maxCubeMapSize{},
+    #ifndef MAGNUM_TARGET_GLES
+    maxRectangleSize{}, maxBufferSize{},
+    #endif
+    maxTextureUnits(0), maxLodBias(0.0f), maxMaxAnisotropy(0.0f), currentTextureUnit(0)
     #ifndef MAGNUM_TARGET_GLES
     , maxColorSamples(0), maxDepthSamples(0), maxIntegerSamples(0), bufferOffsetAlignment(0)
     #endif