readFrameRate only handled .wii files with a text "FrameRate = <value>"
line. Platform .wii files store their config as a 4-byte little-endian
length followed by a "label=value;..." string, with the frame rate
under param.cameraFrameRate, so it returned [] for them.
If the line scan finds nothing, it now reads the length-prefixed config
string and extracts param.cameraFrameRate with a regex. The binary image
data after the config is never read. The length is capped at the file
size so that non-platform files can't trigger an oversized read.
Returns [] if neither format contains a frame rate.
