css: Don't infloop when parsing broken borders

There was an infinite loop when parsing invalid text after having parsed
a color in the border shorthand. See attached testcase for an example.

gtk/gtkcssshorthandpropertyimpl.c

@@ -353,6 +353,13 @@ parse_border_side (GtkCssShorthandProperty  *shorthand,
         if (values[2] == NULL)
           return FALSE;
       }
+    else
+      {
+        /* We parsed and there's still stuff left?
+         * Pretend we didn't notice and let the normal code produce
+         * a 'junk at end of value' error */
+        break;
+      }
   }
   while (!value_is_done_parsing (parser));
 

testsuite/css/parser/Makefile.am

@@ -178,6 +178,9 @@ test_data = \
 	border.ref.css \
 	border-color-currentcolor.css \
 	border-color-currentcolor.ref.css \
+	border-infloop-3.12.css \
+	border-infloop-3.12.errors \
+	border-infloop-3.12.ref.css \
 	border-radius.css \
 	border-radius.errors \
 	border-radius.ref.css \

testsuite/css/parser/border-infloop-3.12.css

@@ -0,0 +1,3 @@
+* {
+  border-bottom: tomato dot;
+}

testsuite/css/parser/border-infloop-3.12.errors

@@ -0,0 +1 @@
+border-infloop-3.12.css:2: error: GTK_CSS_PROVIDER_ERROR_SYNTAX