meson.build: don't condition iconv detection on library detection

meson.build: don't condition iconv detection on library detection

It isn't necessarily the case that use of iconv requires an additional
library. For that reason we shouldn't conditionalize iconv detection on
libiconv.found.

Fixes: 5285e593c33 (configure: Fixes ncursesw detection under msys2/mingw by convert them to meson)
Signed-off-by: Bruce Rogers <brogers@suse.com>
Reviewed-by: Yonggang Luo<l <brogers@suse.com>uoyonggang@gmail.com>
Reviewed-by:Yonggang Luo <luoyonggang@gmail.com>
Message-Id: <20201014221939.196958-1-brogers@suse.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>