pkgsubmit.php: Refactor source processing to fix PHP notice

A foreach() being run without checking to see if the uploaded PKGBUILD had any
sources now no longer causes an undefined index notice when there are no
sources.
Signed-off-by: canyonknight <canyonknight@gmail.com>
Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>

web/html/pkgsubmit.php

@@ -379,9 +379,9 @@ if ($uid):
 			}
 
 			# Insert sources
-			$sources = explode(" ", $new_pkgbuild['source']);
-			foreach ($sources as $src) {
-				if ($src != "" ) {
+			if (!empty($new_pkgbuild['source'])) {
+				$sources = explode(" ", $new_pkgbuild['source']);
+				foreach ($sources as $src) {
 					add_pkg_src($packageID, $src, $dbh);
 				}
 			}