don't crash if rosetta is not available on macOS (#1366)

* don't crash if rosetta is not available on macOS

* make error a dialog

* add newlines

* fix format

* modify strings

kindlecomicconverter/KCC_gui.py

@@ -1189,6 +1189,11 @@ class KCCGUI(KCC_ui.Ui_mainWindow):
             self.kindleGen = False
             if startup:
                 self.display_kindlegen_missing()
+        except OSError as e:
+            self.kindleGen = False
+            if startup:
+                error = f"kindlegen: {e.strerror}\n\n Re-install Rosetta/Kindle Previewer/other Intel app?\n\nPlease email Amazon to make Kindle Previewer Apple silicon native at amazon.com/kindle-help"
+                self.showDialog(error, 'error')
 
     def __init__(self, kccapp, kccwindow):
         global APP, MW, GUI