[gnome-calculator] Fixed zeroth root hang (bgo#775789)

[Robert Roth <robertroth src gnome org>]

commit f5ffca9653df17e1b0101407ae3f767097dfa11d
Author: Robert Roth <robert roth off gmail com>
Date:   Wed Jan 4 01:22:42 2017 +0200

    Fixed zeroth root hang (bgo#775789)

 lib/number.vala |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/lib/number.vala b/lib/number.vala
index cc364a1..d0886d4 100644
--- a/lib/number.vala
+++ b/lib/number.vala
@@ -422,9 +422,12 @@ public class Number : Object
                 p = (uint64) int64.MAX + 1;
             else
                 p = -n;
-        } else {
+        } else if (n > 0) {
             z.num.@set (num);
             p = n;
+        } else {
+            error = _("The zeroth root of a number is undefined.");
+            return new Number.integer (0);
         }
 
         if (!is_complex () && (!is_negative () || (p & 1) == 1))