test: Add test for bad rule in at media block

Based on fuzzing test input generated by Aaron Boxer:
#22

Co-authored-by: John-Mark Bell <[email protected]>

Author: tlsa

test/data/parse2/dodgy-media-block.dat

@@ -7,3 +7,17 @@
 | .outer
 |  top: 0px
 #reset
+
+#data
+@media screen { b; }
+p { padding: 0; }
+#errors
+#expected
+| @media 040
+|  b
+| p
+|  padding-top: 0px
+|  padding-right: 0px
+|  padding-bottom: 0px
+|  padding-left: 0px
+#reset