Prior to this change, if the input string terminates exactly when `len`
characters have been output, the libx52util_convert_utf8_string function
returns an error of `-E2BIG`, even though the buffer is sufficiently
large. Because the output buffer is not expected to be NUL terminated,
this additional character can be safely placed in the output buffer
without overrun.
This change checks for a non-NUL character when the index matches or
exceeds the output buffer length, and only then will it return -E2BIG.
The libx52util_convert_utf8_string function manually converts the UTF-8
string into the character map supported by the X52/X52Pro MFD. However,
there was a bug when handling malformed UTF-8 input. If the state
machine thinks it is at the start of a word and receives malformed UTF-8
input (between 0x80 and 0xC0), it will ignore the characters, but it
will not reset the entry to the map_root location, thereby causing
subsequent characters to be dropped.
This change ensures that the entry is reset to map_root[*input] after
skipping over an invalid UTF-8 sequence.
nirenjan