Merge pull request #351 from caridy/caridy/issue-348

fixes issue #348: perf optimization during diffing algo to avoid calling addVNodes and removeVNodes when there is nothing to do

src/snabbdom.ts

@@ -240,13 +240,15 @@ export function init(modules: Array<Partial<Module>>, domApi?: DOMAPI) {
         }
       }
     }
+    if (oldStartIdx <= oldEndIdx || newStartIdx <= newEndIdx) {
       if (oldStartIdx > oldEndIdx) {
         before = newCh[newEndIdx+1] == null ? null : newCh[newEndIdx+1].elm;
         addVnodes(parentElm, before, newCh, newStartIdx, newEndIdx, insertedVnodeQueue);
-    } else if (newStartIdx > newEndIdx) {
+      } else {
         removeVnodes(parentElm, oldCh, oldStartIdx, oldEndIdx);
       }
     }
+  }
 
   function patchVnode(oldVnode: VNode, vnode: VNode, insertedVnodeQueue: VNodeQueue) {
     let i: any, hook: any;