fix a bug in Text._get_layout that returns an incorrect information for an empty string

svn path=/branches/v0_99_maint/; revision=8135

Author: leejjoon

lib/matplotlib/text.py

@@ -275,8 +275,11 @@ def _get_layout(self, renderer):
         baseline = None
         for i, line in enumerate(lines):
             clean_line, ismath = self.is_math_text(line)
-            w, h, d = renderer.get_text_width_height_descent(
-                clean_line, self._fontproperties, ismath=ismath)
+            if clean_line:
+                w, h, d = renderer.get_text_width_height_descent(
+                    clean_line, self._fontproperties, ismath=ismath)
+            else:
+                w, h, d = 0, 0, 0
             if baseline is None:
                 baseline = h - d
             whs[i] = w, h