emulators/ppsspp: Update to 1.19

• Fix build with system miniupnpc
• Properly use ${LOCALBASE} instead of hardcoding /usr/local for multimedia/ffmpeg3 build dependency
• Misc cleanup (missing USES= flag for desktop-file-utils, correct typo in rapidjson external module commit tag)

Changelog: https://www.ppsspp.org/news/release-1.19/