rhbz#891082: CMXDocument::isSupported: catch exceptions

diff -ru cdr.old/src/lib/CMXDocument.cpp cdr/src/lib/CMXDocument.cpp
--- cdr.old/src/lib/CMXDocument.cpp
+++ cdr/src/lib/CMXDocument.cpp
@@ -46,20 +46,24 @@
 */
 bool libcdr::CMXDocument::isSupported(WPXInputStream *input)
 {
-  input->seek(0, WPX_SEEK_SET);
-  unsigned riff = readU32(input);
-  if (riff != FOURCC_RIFF && riff != FOURCC_RIFX)
-    return false;
-  input->seek(4, WPX_SEEK_CUR);
-  char signature_c = (char)readU8(input);
-  if (signature_c != 'C' && signature_c != 'c')
-    return false;
-  char signature_d = (char)readU8(input);
-  if (signature_d != 'M' && signature_d != 'm')
-    return false;
-  char signature_r = (char)readU8(input);
-  if (signature_r != 'X' && signature_r != 'x')
+  try {
+    input->seek(0, WPX_SEEK_SET);
+    unsigned riff = readU32(input);
+    if (riff != FOURCC_RIFF && riff != FOURCC_RIFX)
+      return false;
+    input->seek(4, WPX_SEEK_CUR);
+    char signature_c = (char)readU8(input);
+    if (signature_c != 'C' && signature_c != 'c')
+      return false;
+    char signature_d = (char)readU8(input);
+    if (signature_d != 'M' && signature_d != 'm')
+      return false;
+    char signature_r = (char)readU8(input);
+    if (signature_r != 'X' && signature_r != 'x')
+      return false;
+  } catch (...) {
     return false;
+  }
   return true;
 }