Wait until getModal returns the correct value

In response to #53

the function is split to two swal and modalDependant

check getmodal if it returns null or not, if it does return null then
start an interval with 100ms until it does not return null and then call
the modalDependant() function, previously swal

lib/sweet-alert.js

@@ -184,6 +184,23 @@
    */
 
   window.sweetAlert = window.swal = function() {
+    // Copy arguments to the local args variable
+    var args = arguments;
+    if (getModal() !== null) {
+        // If getModal returns values then continue
+        modalDependant.apply(this, args);
+    } else {
+        // If getModal returns null i.e. no matches, then set up a interval event to check the return value until it is not null	
+        var modalCheckInterval = setInterval(function() {
+          if (getModal() !== null) {
+            clearInterval(modalCheckInterval);
+            modalDependant.apply(this, args);
+          }
+      }, 100);
+    }
+  };
+
+  function modalDependant() {
 
     // Default parameters
     var params = {