[bugfix, AS] zxbox keyboard input overflows text variable
int zx_kbd_input(char* text/*, int buflen*/)
is supplied with a single char by all callers
thats fine till we get to here in the decode routine
while (*utf8)
since it just reads till it hits a 0 its probably fine
but Address Sanitizer caught it
make c a char array of 8 bytes to ensure a NULL
Change-Id: Iad3284df34cb7451422fc96ae0bb8e159ee440b0