fix defaults for microED extinction coeffs.

Author: vondreele

GSASII/GSASIIddataGUI.py

@@ -940,7 +940,7 @@ def OnFixVals(event):
                 UseList[G2frame.hist]['Extinction'][2].update({'Ma':[1.0,False]})
                 UseList[G2frame.hist]['Extinction'][2].update({'Mb':[0.0,False]})
             if 'Mc' not in UseList[G2frame.hist]['Extinction'][2]:
-                UseList[G2frame.hist]['Extinction'][2].update({'Mc':[1.0,False]})
+                UseList[G2frame.hist]['Extinction'][2].update({'Mc':[0.0,False]})
         elif 'PWDR' in UseList[G2frame.hist]['Histogram']:
             if 'LeBail' not in UseList[G2frame.hist]:
                 UseList[G2frame.hist]['LeBail'] = False