throw an exception only on Android if File::unlock has failed

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Enhancements
 * <New feature description> (PR [#????](https://github.com/realm/realm-core/pull/????))
 * Added support for server log messages that are enabled by sync protocol version 10. Appservices request id will be provided in a server log message in a future server release. ([PR #6476](https://github.com/realm/realm-core/pull/6476))
+* Throw an exception if `File::unlock` has failed, in order to inform the SDK that we are likely hitting some limitation on the OS filesystem, instead of crashing the application.([PR #6926](https://github.com/realm/realm-core/pull/6926))
 
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)

src/realm/util/file.cpp

@@ -1098,7 +1098,10 @@ static void _unlock(int m_fd)
     do {
         r = flock(m_fd, LOCK_UN);
     } while (r != 0 && errno == EINTR);
-    REALM_ASSERT_RELEASE_EX(r == 0 && "File::unlock()", r, errno);
+    if (r && errno) {
+        throw RuntimeError(ErrorCodes::RuntimeError,
+                           "File::unlock() has failed, this is likely due to some limitation in the OS file system.");
+    }
 }
 #endif