Don't crash if source is empty/unsupplied

Fixes #38.

Author: usmonster

index.html

@@ -108,7 +108,7 @@ <h2>
 							<code>source</code>
 						</td>
 						<td>
-							null
+							[]
 						</td>
 						<td>
 							Array, String (url)

js/jquery.fn.gantt.js

@@ -31,7 +31,7 @@
         var scales = ["hours", "days", "weeks", "months"];
         //Default settings
         var settings = {
-            source: null,
+            source: [],
             itemsPerPage: 7,
             months: ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
             dow: ["S", "M", "T", "W", "T", "F", "S"],
@@ -1449,7 +1449,7 @@
                         maxDate = maxDate < tools.dateDeserialize(date.to) ? tools.dateDeserialize(date.to) : maxDate;
                     });
                 });
-
+                maxDate = maxDate || new Date();
                 switch (settings.scale) {
                     case "hours":
                         maxDate.setHours(Math.ceil((maxDate.getHours()) / element.scaleStep) * element.scaleStep);
@@ -1482,6 +1482,7 @@
                         minDate = minDate > tools.dateDeserialize(date.from) || minDate === null ? tools.dateDeserialize(date.from) : minDate;
                     });
                 });
+                minDate = minDate || new Date();
                 switch (settings.scale) {
                     case "hours":
                         minDate.setHours(Math.floor((minDate.getHours()) / element.scaleStep) * element.scaleStep);