AZW3 Input: Fix crash when processing AZW3 files that contain certain SVG images dies to a bug in ImageMagick. See #1384375 (svg cover lost when converting ePub->AZW3)

src/calibre/utils/imghdr.py

@@ -10,10 +10,10 @@ def what(file, h=None):
     if h is None:
         if isinstance(file, basestring):
             f = open(file, 'rb')
-            h = f.read(44)
+            h = f.read(150)
         else:
             location = file.tell()
-            h = file.read(44)
+            h = file.read(150)
             file.seek(location)
             f = None
     else:
@@ -132,6 +132,12 @@ def test_emf(h, f):
 
 tests.append(test_emf)
 
+def test_svg(h, f):
+    if (h[:2] == b'<?' and h[2:5].lower() == 'xml' and b'<svg' in h) or h.startswith(b'<svg'):
+        return 'svg'
+
+tests.append(test_svg)
+
 # --------------------#
 # Small test program #
 # --------------------#

src/calibre/utils/magick/draw.py

@@ -137,6 +137,9 @@ def identify_data(data):
     (width, height, format)
     or raises an Exception if data is not an image.
     '''
+    if data.startswith(b'<?xml'):
+        # ImageMagick segfaults when trying to identify SVG images
+        raise ValueError('Identifying svg images is not supported')
     img = Image()
     if hasattr(img, 'identify'):
         img.identify(data)