BUG: set correct xlims for lines (pandas-dev#11471, pandas-dev#11310)

 * Do not assume that xdata is sorted.
 * Use numpy.nanmin() and numpy.nanmax() instead.

Author: nmartensen

pandas/plotting/_tools.py

@@ -362,8 +362,8 @@ def _get_xlim(lines):
     left, right = np.inf, -np.inf
     for l in lines:
         x = l.get_xdata(orig=False)
-        left = min(x[0], left)
-        right = max(x[-1], right)
+        left = min(np.nanmin(x), left)
+        right = max(np.nanmax(x), right)
     return left, right