MNT: Ensure positive interval for timers

Some backends don't handle 0 interval timers, so we can just set
a minimum of 1 millisecond for the resolution of the timer to ensure
a positive interval passed to all backend timers.

Author: greglucas

lib/matplotlib/backend_bases.py

@@ -1164,7 +1164,8 @@ def interval(self):
     def interval(self, interval):
         # Force to int since none of the backends actually support fractional
         # milliseconds, and some error or give warnings.
-        interval = int(interval)
+        # Some backends also fail when interval == 0, so ensure >= 1 msec
+        interval = max(int(interval), 1)
         self._interval = interval
         self._timer_set_interval()