applied proposals of #267 by @diegocr

Author: woolfg

jspdf.plugin.addimage.js

@@ -174,8 +174,8 @@
 
 		if(element.nodeName === 'CANVAS') {
 			var canvas = element;
-		//if already a supported data url image, just return the dataurl
-		} else if (element.getAttribute('src').indexOf('data:image/') === 0) {
+		//if element is an image which uses data url defintion, just return the dataurl
+		} else if (element.nodeName === 'IMG' && element.getAttribute('src') && element.getAttribute('src').indexOf('data:image/') === 0) {
 			return element.getAttribute('src');	
 		} else {
 			var canvas = document.createElement('canvas');

jspdf.plugin.from_html.js

@@ -438,9 +438,9 @@
 					if (img.width + img.height) {
 						images[url] = images[url] || img;
 					}
-					if(!--x) {
-						done();
-					}
+				}
+				if(!--x) {
+					done();
 				}
 			};
 			img.src = url;