Refactored check in IGListCollectionViewLayout for more reliable cove…

…rage

Summary:
The `[context invalidateDataSourceCounts] && _minimumInvalidatedSection == NSNotFound` condition was never getting triggered in any of our tests.

I tried to simulate this condition in my testing, but it doesn't seem possible to have `_minimumInvalidatedSection` set to `NSNotFound` when execution reaches this point. This is because the only public pathway I could see to `[context invalidateLayoutWithContext:]` was via the regular `invalidateLayout` method which always sets `_minimumInvalidatedSection` to 0 before continuing.

To solve this, since the resulting logic ends up being the same in the check above, I simply collapsed this check into the one above it.

Reviewed By: fabiomassimo

Differential Revision: D50000788

fbshipit-source-id: da0bf0cb16c98de95f802dfd35bbdf0e935e615f

Source/IGListKit/IGListCollectionViewLayout.mm

@@ -389,12 +389,10 @@ - (void)invalidateLayoutWithContext:(IGListCollectionViewLayoutInvalidationConte
 
     if (hasInvalidatedItemIndexPaths
         || [context invalidateEverything]
+        || ([context invalidateDataSourceCounts] && _minimumInvalidatedSection == NSNotFound) // if count changed and we don't have information on the minimum invalidated section
         || context.ig_invalidateAllAttributes) {
         // invalidates all
         _minimumInvalidatedSection = 0;
-    } else if ([context invalidateDataSourceCounts] && _minimumInvalidatedSection == NSNotFound) {
-        // invalidate all if count changed and we don't have information on the minimum invalidated section
-        _minimumInvalidatedSection = 0;
     }
 
     if (context.ig_invalidateSupplementaryAttributes) {