Add check for semi-colon existence in theme file comment lines

- Address https://github.com/friendica/friendica/issues/8000#issuecomment-592946450

src/Core/Theme.php

@@ -98,7 +98,7 @@ class Theme
 			$comment_lines = explode("\n", $matches[0]);
 			foreach ($comment_lines as $comment_line) {
 				$comment_line = trim($comment_line, "\t\n\r */");
-				if ($comment_line != "") {
+				if (strpos($comment_line, ':') !== false) {
 					list($key, $value) = array_map("trim", explode(":", $comment_line, 2));
 					$key = strtolower($key);
 					if ($key == "author") {