fix(utils): Fix autogenerated grid coords

Fixes react-grid-layout#368, broken by eac7e08

Author: STRML

lib/utils.js

@@ -359,11 +359,12 @@ export function synchronizeLayoutWithChildren(initialLayout: Layout, children: R
   initialLayout = initialLayout || [];
 
   // Generate one layout item per child.
-  let layout: Layout = React.Children.map(children, (child: React.Element<any>) => {
+  let layout: Layout = [];
+  React.Children.forEach(children, (child: React.Element<any>, i: number) => {
     // Don't overwrite if it already exists.
     const exists = getLayoutItem(initialLayout, child.key || "1" /* FIXME satisfies Flow */);
     if (exists) {
-      return cloneLayoutItem(exists);
+      layout[i] = cloneLayoutItem(exists);
     } else {
       if (process.env.NODE_ENV !== 'production' && child.props._grid) {
         console.warn('`_grid` properties on children have been deprecated as of React 15.2. ' + // eslint-disable-line
@@ -377,10 +378,11 @@ export function synchronizeLayoutWithChildren(initialLayout: Layout, children: R
           validateLayout([g], 'ReactGridLayout.children');
         }
 
-        return cloneLayoutItem({...g, i: child.key});
+        layout[i] = cloneLayoutItem({...g, i: child.key});
+      } else {
+        // Nothing provided: ensure this is added to the bottom
+        layout[i] = cloneLayoutItem({w: 1, h: 1, x: 0, y: bottom(layout), i: child.key || "1"});
       }
-      // Nothing provided: ensure this is added to the bottom
-      return cloneLayoutItem({w: 1, h: 1, x: 0, y: bottom(layout), i: child.key || "1"});
     }
   });