TextureCache: Ensure that all render target textures have as many layers as the frame buffer.

Also fixes a case where the D3D code path did not initialize num_layers leading to undefined behaviour.

Source/Core/VideoCommon/FramebufferManagerBase.cpp

@@ -12,6 +12,8 @@ const XFBSourceBase* FramebufferManagerBase::m_overlappingXFBArray[MAX_VIRTUAL_X
 unsigned int FramebufferManagerBase::s_last_xfb_width = 1;
 unsigned int FramebufferManagerBase::s_last_xfb_height = 1;
 
+unsigned int FramebufferManagerBase::m_EFBLayers = 1;
+
 FramebufferManagerBase::FramebufferManagerBase()
 {
 	m_realXFBSource = nullptr;