glslang -> SPV: fix degenerate switch topologies (bug 14118).

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@31485 e7fa87d3-cd2b-0410-9028-fcbf551c1848

Test/spv.switch.frag

@@ -130,4 +130,13 @@ void main()
 
     color += foo1(v,v,c).y;
     color += foo2(v,v,c).z;
+
+    switch (c) {
+    case 0: break;
+    default:
+    }
+
+    switch (c) {
+    default:
+    }
 }