Fix segfault in HTTP handler.

[Wilm0r]

dump1090 crashes when a non-existent file with no dot in its name is requested. strrchr() will return NULL, not an empty string, when there is no match.

[steel101]

just inserted the code in to my fork it has this and plane count and plane count in title and signal and settings page and lots more including almost all pull request here demo at http://bitropy.net:8080