Dont require pattern lib if hatch cant be understood

Author: MadsAdrian

tikzplotlib/_hatches.py

@@ -90,15 +90,15 @@ def _mpl_hatch2pgfp_pattern(data, hatch, color_name, color_rgba):
         Output:
             draw_options - list, empty or with a post action string
     """
-    data["tikz libs"].add("patterns")
-
     hatch = __validate_hatch(hatch)
     try:
         pgfplots_pattern = _MP_HATCH2PGF_PATTERN.get(hatch)
     except KeyError:
         warnings.warn("tikzplotlib: The hatch", hatch, "is ignored.")
         return data, []
 
+    data["tikz libs"].add("patterns")
+
     pattern_options = [f"pattern={pgfplots_pattern}"]
     if color_name != "black":
         # PGFPlots render patterns in 'pattern color' (default: black)