svg: added fallback mime by file ext

for handling unorthodox svg-xml  variants

src/Products/CMFCore/FSImage.py

@@ -81,6 +81,8 @@ def _readFile(self, reparse):
                 self.ZCacheable_invalidate()
                 self._file_mod_time = mtime
             ct, width, height = getImageInfo(data)
+            if ct == '' and self.id.endswith('.svg'):
+                ct = 'image/svg+xml'
             self.content_type = ct
             self.width = width
             self.height = height