Rendering fails when infinite values are present

[Michael Leinartas]

Rendering graphs fails if any of the points contains an 'inf' value (possible when "inf" or "Infinity" is passed as a value to carbon).

Here's the stacktrace:

    Traceback (most recent call last):
      File "/usr/lib/pymodules/python2.7/django/core/handlers/base.py", line 100, in get_response
        response = callback(request, *callback_args, **callback_kwargs)
      File "/opt/graphite/webapp/graphite/render/views.py", line 166, in renderView
        image = doImageRender(requestOptions['graphClass'], graphOptions)
      File "/opt/graphite/webapp/graphite/render/views.py", line 338, in doImageRender
        img = graphClass(**graphOptions)
      File "/opt/graphite/webapp/graphite/render/glyph.py", line 174, in __init__
        self.drawGraph(**params)
      File "/opt/graphite/webapp/graphite/render/glyph.py", line 515, in drawGraph
        self.setupYAxis()
      File "/opt/graphite/webapp/graphite/render/glyph.py", line 867, in setupYAxis
        self.yLabelWidth = max([self.getExtents(label)['width'] for label in self.yLabels])
    ValueError: max() arg is an empty sequence

Modifying the safeMax et al functions to filter out 'inf' values resolves the issue for me

[Michael Leinartas (mleinartas)]

Fix committed in r703