Fix empty locale errors in format_number/percent

If our format_number() and format_percent() wrappers (around the babel
functions) aren't passed a locale argument, they will use c.locale. But
in some cases, c.locale will return an empty string, which will then be
used when calling the babel functions. The locale-parsing in babel is
unable to handle an empty string, and will throw an exception.

This commit changes these wrappers slightly so that if c.locale is also
empty, the wrappers will instead call the babel functions without a
locale argument, which will cause it to default to the LC_NUMERIC
environment variable.

r2/r2/lib/template_helpers.py

@@ -663,11 +663,20 @@ def format_number(number, locale=None):
     if not locale:
         locale = c.locale
 
-    return babel.numbers.format_number(number, locale=locale)
+    if locale:
+        return babel.numbers.format_number(number, locale=locale)
+    else:
+        return babel.numbers.format_number(number)
 
 
 def format_percent(ratio, locale=None):
-    return babel.numbers.format_percent(ratio, locale=locale or c.locale)
+    if not locale:
+        locale = c.locale
+
+    if locale:
+        return babel.numbers.format_percent(ratio, locale=locale)
+    else:
+        return babel.numbers.format_percent(ratio)
 
 
 def html_datetime(date):