Fix C99 errors uncovered by -Wint-conversion and -Werror,-Wincompatib…

[NHOrus]

…le-pointer-types

Fixes downstream bug https://bugs.gentoo.org/886460

[rouault]

This fix doesn't seem to be correct to me. os_case() prototype is char *os_case( char *filename ), and coverage is already a char*, so there is no need to take its address

[NHOrus]

It's weird, but both Clang and GCC were giving errors:

../vpfprop.c:1474:27: error: incompatible integer to pointer conversion passing 'char' to parameter of type 'char *'; take the address with & [-Wint-conversion]
   strcat(covpath,os_case(coverage));
                          ^~~~~~~~
                          &

yeah, thank you.

It's bad fix, due to

ogdi/vpflib/vpfprop.c

Line 1449 in 8319fdc

char *library_path, coverage;

hitting line without pointer declared.

[NHOrus]

New commit should have good fix.
Sorry.