Use generic sans serif font as preview font

During the settings initialization, a QApplication is not yet
constructed, and QFont() just returns the first font in list instead
of the right one.

(cherry picked from commit 3e43d45)

Author: mitya57

ReText/__init__.py

@@ -162,7 +162,9 @@ def __setattr__(self, option, value):
 	def __getattribute__(self, option):
 		value = object.__getattribute__(self, option)
 		# Choose a font just-in-time, because when the settings are
-		# loaded it is too early to work on Windows
+		# loaded it is too early to work.
+		if option == 'font' and not value.family():
+			value = QFont()
 		if option == 'editorFont' and not value.family():
 			value = chooseMonospaceFont()
 		return value