Fix most clang warnings

- member initializing order in some constructors
- missing default branches in switch-case
- uninitialized variable if switch-case default (uncritical because
  program would exit)
- && and || brace warnings in if()

glslang/MachineIndependent/Versions.cpp

@@ -457,6 +457,8 @@ bool TParseContext::extensionsTurnedOn(int numExtensions, const char* const exte
         case EBhRequire:
         case EBhWarn:
             return true;
+        default:
+            break;
         }
     }