perform Fourier phase checks only if a Fourier block is present and not set to power spectra.

src/classes/PMsrHandler.cpp

@@ -6723,7 +6723,11 @@ Bool_t PMsrHandler::CheckRRFSettings()
  */
 Bool_t PMsrHandler::CheckRealFFT()
 {
-  // check 	
+  // if no Fourier block is present, nothing needs to be checked
+  if (!fFourier.fFourierBlockPresent)
+    return true;
+
+  // if Fourier is set to power spectra, no phase checks are needed
   if (fFourier.fPlotTag == FOURIER_PLOT_POWER)
     return true;