Replace assertion with an error message.

src/tiffcomposite_int.cpp

@@ -1540,7 +1540,11 @@ namespace Exiv2 {
         for (auto&& component : components_) {
             if (component->tag() == 0x014a) {
                 // Hack: delay writing of sub-IFD image data to get the order correct
-                assert(pSubIfd == 0);
+#ifndef SUPPRESS_WARNINGS
+                if (pSubIfd != 0) {
+                    EXV_ERROR << "Multiple sub-IFD image data tags found\n";
+                }
+#endif
                 pSubIfd = component;
                 continue;
             }

tests/bugfixes/github/test_issue_1847.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+
+from system_tests import CaseMeta, path, check_no_ASAN_UBSAN_errors
+
+class TiffMnEntryDoCountInvalidTiffType(metaclass=CaseMeta):
+    """
+    Test for the bug described in:
+    https://github.com/Exiv2/exiv2/issues/1847
+    """
+    url = "https://github.com/Exiv2/exiv2/issues/1847"
+
+    filename = path("$data_path/issue_1847_poc.jpg")
+    commands = ["$exiv2 -pS $filename"]
+    stderr = [""]
+    retval = [0]
+
+    compare_stdout = check_no_ASAN_UBSAN_errors