cmPrefs.h/c Check existsFl prior to signaling kDuplicateIdPrRC error in _cmPrefsCreateJsonNode().

cmPrefs.c

     pnp->id = _cmPrefsCalcNextAvailId(p);
   else
   {
-    if( _cmPrefsIdToNodePtr(p, id, false ) != NULL )
-      cmErrWarnMsg(&p->err,kDuplicateIdPrRC,"The preference variable id '%i' is used by multiple preference variables including '%s'.",id,cmStringNullGuard(pathString));
+    if( existsFl == false )
+      if( _cmPrefsIdToNodePtr(p, id, false ) != NULL )
+        cmErrWarnMsg(&p->err,kDuplicateIdPrRC,"The preference variable id '%i' is used by multiple preference variables including '%s'.",id,cmStringNullGuard(pathString));
   
     pnp->id = id;
   }

cmPrefs.h

   cmPrRC_t cmPrefsPathSetString( cmPrH_t h, const cmChar_t* pathStr, const cmChar_t* val );
 
   // Create a new preference variable and set it's value to 'val'.
-  // If a variable with the same path and type already exists and kForceValuePrFl is set then update it's value to 'val'.
-  // Note that in this case if kForceValuePrFl is not set then the function returns quietly.
+  // If a variable with the same path and type already exists and kForceValuePrFl
+  // is set then update it's value to 'val'. Note that in this case if
+  //  kForceValuePrFl is not set then the function returns quietly.
   //
   // If a variable with the same path but a different type exists then an error is returned.
   //