Fixed restarting cell to (-) type. Added a final point to the while cycle.

IPython/nbconvert/preprocessors/revealhelp.py

@@ -55,14 +55,16 b' class RevealHelpPreprocessor(Preprocessor):'
                     worksheet.cells[index - 1].metadata.slide_helper = 'slide_end'
                 if cell.metadata.slide_type in ['subslide']:
                     worksheet.cells[index - 1].metadata.slide_helper = 'subslide_end'
+                #Prevent the rendering of "do nothing" cells before fragments
                 if cell.metadata.slide_type in ['fragment']:
-                    try:
                         i = 1
-                        while 1:
+                    while i < len(worksheet.cells) - index:
                             worksheet.cells[index + i].metadata.frag_helper = 'fragment_end'
                             i += 1
-                    except IndexError as e:
-                        pass #Last cell doesn't have a next one
+                #Restart the slide_helper when the cell status is changed
+                #to "do nothing".
+                if cell.metadata.slide_type in ['-']:
+                    worksheet.cells[index - 1].metadata.slide_helper = '-'
 
         if not isinstance(resources['reveal'], dict):
             resources['reveal'] = {}