Bug 452438 - Null-check stored printer-name string before passing it to nsTSubstring::Equals(), to avoid triggering an assertion. r+sr=roc

widget/src/gtk2/nsPrintSettingsGTK.cpp

@@ -491,7 +491,12 @@ nsPrintSettingsGTK::SetPrinterName(const PRUnichar * aPrinter)
     gtkPrinter.Cut(0, strlen("CUPS/"));
   }
 
-  if (!gtkPrinter.Equals(gtk_print_settings_get_printer(mPrintSettings))) {
+  // Give mPrintSettings the passed-in printer name if either...
+  // - it has no printer name stored yet
+  // - it has an existing printer name that's different from
+  //   the name passed to this function.
+  const char* oldPrinterName = gtk_print_settings_get_printer(mPrintSettings);
+  if (!oldPrinterName || !gtkPrinter.Equals(oldPrinterName)) {
     mIsInitedFromPrinter = PR_FALSE;
     mIsInitedFromPrefs = PR_FALSE;
     gtk_print_settings_set_printer(mPrintSettings, gtkPrinter.get());