Fixed CompileSet so it returns true when there is nothing to compile at all.

src/osgUtil/IncrementalCompileOperation.cpp

@@ -441,7 +441,7 @@ bool IncrementalCompileOperation::CompileSet::compile(CompileInfo& compileInfo)
             return _numberCompileListsToCompile==0;
         }
     }
-    return false;
+    return _numberCompileListsToCompile==0;
 }
 
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