Fix potential crash when setting a datablock to have no textures

As a precondition, the datablock must've had textures before, the
datablock ended up fully loaded and baked with textures, and not be
running on OpenGL.

Components/Hlms/Common/include/OgreHlmsTextureBaseClass.inl

@@ -288,9 +288,15 @@ namespace Ogre
         else if( !mSamplersDescSet || *mSamplersDescSet != baseSampler )
         {
             if( mSamplersDescSet )
+            {
                 hlmsManager->destroyDescriptorSetSampler( mSamplersDescSet );
-            mSamplersDescSet = hlmsManager->getDescriptorSetSampler( baseSampler );
-            needsRecalculateHash = true;
+                mSamplersDescSet = 0;
+            }
+            if( !baseSampler.mSamplers.empty() )
+            {
+                mSamplersDescSet = hlmsManager->getDescriptorSetSampler( baseSampler );
+                needsRecalculateHash = true;
+            }
         }
 
         return needsRecalculateHash;