Credit to OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=37492

Throw an error if the size of the preview is greater than 1MB.

src/tiffvisitor_int.cpp

@@ -1598,6 +1598,9 @@ namespace Exiv2 {
         if ( !isize ) {
             v->read(pData, size, byteOrder());
         } else {
+            // Prevent large memory allocations: https://github.com/Exiv2/exiv2/issues/1881
+            enforce(isize <= 1024 * 1024, kerCorruptedMetadata);
+
             // #1143 Write a "hollow" buffer for the preview image
             //       Sadly: we don't know the exact location of the image in the source (it's near offset)
             //       And neither TiffReader nor TiffEntryBase have access to the BasicIo object being processed