Fix flash of 'Not found' error message when fetching a reusable block

Re-order the FETCH_REUSABLE_BLOCKS effect so that the reusable block is
added to the store before it is marked as no longer being fetched. This
prevents core/block from briefly flashing the 'Not found' error message
in between dispatches.

editor/store/effects.js

@@ -347,18 +347,18 @@ export default {
 
 		result.then(
 			( reusableBlockOrBlocks ) => {
-				dispatch( {
-					type: 'FETCH_REUSABLE_BLOCKS_SUCCESS',
-					id,
-				} );
-
 				dispatch( receiveReusableBlocks( map(
 					castArray( reusableBlockOrBlocks ),
 					( reusableBlock ) => ( {
 						reusableBlock,
 						parsedBlock: parse( reusableBlock.content )[ 0 ],
 					} )
 				) ) );
+
+				dispatch( {
+					type: 'FETCH_REUSABLE_BLOCKS_SUCCESS',
+					id,
+				} );
 			},
 			( error ) => {
 				dispatch( {