dirLength == 0 can cause an infinite loop.

src/image.cpp

@@ -334,6 +334,8 @@ namespace Exiv2 {
                 throw Error(kerCorruptedMetadata);
             }
             uint16_t   dirLength = byteSwap2(dir,0,bSwap);
+            // Prevent infinite loops. (GHSA-m479-7frc-gqqg)
+            enforce(dirLength > 0, kerCorruptedMetadata);
 
             if ( dirLength > 500 ) // tooBig
                 throw Error(kerTiffDirectoryTooLarge);