Avoid crashing on stdDeviation attribute

Signed-off-by: Niels Thykier <niels@thykier.net>

scour/scour.py

@@ -1862,7 +1862,8 @@ default_attributes = [
     DefaultAttribute('seed', 0, elements=['feTurbulence']),
     DefaultAttribute('specularConstant', 1, elements=['feSpecularLighting']),
     DefaultAttribute('specularExponent', 1, elements=['feSpecularLighting', 'feSpotLight']),
-    DefaultAttribute('stdDeviation', 0, elements=['feGaussianBlur']),
+    # Pretend it is a string (for the same reasons as we do with "order")
+    DefaultAttribute('stdDeviation', '0', elements=['feGaussianBlur']),
     DefaultAttribute('stitchTiles', 'noStitch', elements=['feTurbulence']),
     DefaultAttribute('surfaceScale', 1, elements=['feDiffuseLighting', 'feSpecularLighting']),
     DefaultAttribute('type', 'matrix', elements=['feColorMatrix']),

testscour.py

@@ -1580,6 +1580,16 @@ class RemoveDefaultAttributeOrderSVGLengthCrash(unittest.TestCase):
             self.fail("Processing the order attribute triggered an AttributeError")
 
 
+class RemoveDefaultAttributeStdDeviationSVGLengthCrash(unittest.TestCase):
+
+    # Triggered a crash in v0.36
+    def runTest(self):
+        try:
+            scourXmlFile('unittests/remove-default-attr-std-deviation.svg')
+        except AttributeError:
+            self.fail("Processing the order attribute triggered an AttributeError")
+
+
 class CDATAInXml(unittest.TestCase):
 
     def runTest(self):

unittests/remove-default-attr-std-deviation.svg

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink= "http://www.w3.org/1999/xlink">
+  <defs>
+    <filter id="filter" filterUnits="objectBoundingBox" x="0%" y="0%" width="100%" height="100%">
+      <feGaussianBlur stdDeviation="0 0" x="10" y="10" dx="20" dy="20" />
+    </filter>
+  </defs>
+  <!-- Use the filter (otherwise, scour discards it before it trips over it) -->
+  <image id="png" x="10" y="30" width="150" height="50" xlink:href="raster.png"
+         filter="url(#filter)"/>
+</svg>