Fix path_effects to work on text with spaces only

When a line of text contains no visual output (spaces only or empty
newlines), there is no path to create for the effects. So, the data
array for this non-path does not have the commonly expected shape for a
path, so the logic bails with an error.

The solution is, do not try to draw a path when the text string has
only spaces and newlines.

closes matplotlib#22687

Author: has2k1

lib/matplotlib/patheffects.py

@@ -138,6 +138,9 @@ def draw_path_collection(self, gc, master_transform, paths, *args,
                                           *args, **kwargs)
 
     def _draw_text_as_path(self, gc, x, y, s, prop, angle, ismath):
+        if not s.strip():
+            return
+
         # Implements the naive text drawing as is found in RendererBase.
         path, transform = self._get_text_path_transform(x, y, s, prop,
                                                         angle, ismath)

lib/matplotlib/tests/baseline_images/test_patheffects/spaces_and_newlines.png

@@ -189,3 +189,16 @@ def test_tickedstroke():
 
     ax3.set_xlim(0, 4)
     ax3.set_ylim(0, 4)
+
+
+@image_comparison(['spaces_and_newlines.png'], remove_text=True)
+def test_patheffects_spaces_and_newlines():
+    ax = plt.subplot()
+    s1 = "         "
+    s2 = "\nNewline also causes problems"
+    text1 = ax.text(0.5, 0.75, s1, ha='center', va='center', size=20,
+                    bbox={'color': 'salmon'})
+    text2 = ax.text(0.5, 0.25, s2, ha='center', va='center', size=20,
+                    bbox={'color': 'thistle'})
+    text1.set_path_effects([path_effects.Normal()])
+    text2.set_path_effects([path_effects.Normal()])