Fix nbrun in notebooks with non-code cells.

IPython/core/interactiveshell.py

@@ -2568,7 +2568,8 b' class InteractiveShell(SingletonConfigurable):'
                     if not nb.worksheets:
                         return
                     for cell in nb.worksheets[0].cells:
-                        yield cell.input
+                        if cell.cell_type == 'code':
+                            yield cell.input
             else:
                 with open(fname) as f:
                     yield f.read()