Actually fix NPE source.

Wont ask the cover if it has such capability if the entity itself doesnt have it on that side.
null check in cover capability code wont trigger anymore

src/main/java/gregtech/api/metatileentity/MetaTileEntity.java

@@ -771,6 +771,10 @@ public final <T> T getCoverCapability(Capability<T> capability, EnumFacing side)
         boolean isCoverable = capability == GregtechTileCapabilities.CAPABILITY_COVERABLE;
         CoverBehavior coverBehavior = side == null ? null : getCoverAtSide(side);
         T originalCapability = getCapability(capability, side);
+        // If we have no such capability on this side, then the cover on this side cant have it either
+        if (originalCapability == null) {
+            return null;
+        }
         if (coverBehavior != null && !isCoverable) {
             return coverBehavior.getCapability(capability, originalCapability);
         }