MDL-50963 lang/en/grades.php: Improve bad grade error message

The error message received when inputting a grade value that is too
low indicates that zero is a valid grade value. This is incorrect as
the lowest valid grade value is 1. This updates the error message to
indicate the minimum acceptable grade value is 1, not 0.

lang/en/grades.php

@@ -470,7 +470,7 @@
 $string['missingitemtypeoreid'] = 'Array key (itemtype or eid) missing from 2nd param of grade_edit_tree_column_select::get_item_cell($item, $params)';
 $string['missingscale'] = 'Scale must be selected';
 $string['mode'] = 'Mode';
-$string['modgradeerrorbadpoint'] = 'Invalid Grade Value. This must be an integer between 0 and {$a}';
+$string['modgradeerrorbadpoint'] = 'Invalid Grade Value. This must be an integer between 1 and {$a}';
 $string['modgradeerrorbadscale'] = 'Invalid scale selected. Please make sure you select a scale from the selections below.';
 $string['modgrade'] = 'Grade';
 $string['modgrade_help'] = 'Select the type of grading used for this activity. If "scale" is chosen, you can then choose the scale from the "scale" dropdown. If using "point" grading, you can then enter the maximum grade available for this activity.';