Fix issue w/ invalid context settings (fixes #348)

Author: lukelbd

WHATSNEW.rst

@@ -247,6 +247,8 @@ Bug fixes
   `~proplot.colors.DiscreteColormap` incorrectly samples the color list (:issue:`299`).
 * Fix issue where `~proplot.axes.Axes.legend` ignores the user-input `fontsize`
   (:issue:`331`).
+* Fix issue where passing invalid rc setting to ``.format`` results in persistent
+  invalid `rc` state requiring restarting the session/configurator (:issue:`348`).
 * Fix issue where ``proplotrc`` settings are ignored if a subsequent line contains
   an overlapping meta-setting (:issue:`333`).
 * Fix issue where setting :rcraw:`legend.facecolor` or :rcraw:`legend.edgecolor` to

proplot/config.py

@@ -790,7 +790,11 @@ def __enter__(self):
         rc_new = context.rc_new  # used for context-based _get_item_context
         rc_old = context.rc_old  # used to re-apply settings without copying whole dict
         for key, value in kwargs.items():
-            kw_proplot, kw_matplotlib = self._get_item_dicts(key, value)
+            try:  # TODO: consider moving setting validation to .context()
+                kw_proplot, kw_matplotlib = self._get_setting_dicts(key, value)
+            except ValueError as error:
+                self.__exit__()
+                raise error
             for rc_dict, kw_new in zip(
                 (rc_proplot, rc_matplotlib),
                 (kw_proplot, kw_matplotlib),