qbsp: fix "sides not found" warning spam in Q1 maps with sky

fixes #366

common/bspfile.cc

@@ -697,6 +697,10 @@ public:
         auto bits_a = contentflags_to_bits(a);
         auto bits_b = contentflags_to_bits(b);
 
+        // aviods spamming "sides not found" warning on Q1 maps with sky
+        if ((bits_a.solid || bits_a.sky) && (bits_b.solid || bits_b.sky))
+            return create_empty_contents();
+
         q1_contentflags_bits result;
 
         if (bits_a.suppress_clipping_same_type || bits_b.suppress_clipping_same_type) {

testmaps/qbsp_simple_worldspawn_sky.map

@@ -67,3 +67,8 @@
 "classname" "info_player_start"
 "origin" "-88 -64 120"
 }
+// entity 2
+{
+"classname" "info_null"
+"origin" "-40 -48 152"
+}

tests/test_qbsp.cc

@@ -727,6 +727,8 @@ TEST_CASE("simple_worldspawn_sky" * doctest::test_suite("testmaps_q1"))
 
     CHECK(prt->portals.size() == 0);
     // FIXME: unsure what the expected number of visclusters is, does sky get one?
+
+    CHECK(12 == bsp.dclipnodes.size());
 }
 
 TEST_CASE("water_detail_illusionary" * doctest::test_suite("testmaps_q1"))