typefindfunctions: Fix otio typefinder
memcmp() returns 0 (aka FALSE) on match and a difference otherwise.
Previously the typefinder was matching on anything but otio files that happened to have some curly braces in the beginning of the file.
Fixes a false positive with a MOV file.
CC @thiblahute Please test this with a valid OTIO file. I assume the previous typefinder somehow worked for valid files, so most likely it is broken in a different way now and does not detect them anymore.