Avoid gcc: "specified bound depends on the length of the source argument"

Just use memcpy().

Change-Id: Icb705acb6c12baf28684c763a77da7abc514ea6d
Reviewed-on: https://gerrit.libreoffice.org/57714
Tested-by: Jenkins
Reviewed-by: Tor Lillqvist <tml@collabora.com>

include/LibreOfficeKit/LibreOfficeKitInit.h

@@ -200,7 +200,7 @@ static void *lok_dlopen( const char *install_path, char ** _imp_lib )
         return NULL;
     }
 
-    strncpy(imp_lib, install_path, imp_lib_size);
+    memcpy(imp_lib, install_path, partial_length);
 
     extendUnoPath(install_path);