qtcreatorcdbext: Fix qbs build for the "no python" case

Change-Id: Ic62b1052ffa693c0a040de1a2efd2dc06b49ac7f
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/qtcreatorcdbext/qtcreatorcdbext.qbs

@@ -122,7 +122,10 @@ QtcLibrary {
         ]
     }
 
-    cpp.defines: ["WITH_PYTHON=1"]
+    Properties {
+        condition: pythonDllProbe.found
+        cpp.defines: ["WITH_PYTHON=1"]
+    }
     cpp.includePaths: {
         var paths = [FileInfo.joinPaths(cdbPath, "inc")];
         if (pythonDllProbe.found)