analyze: use '' instead of the empty string when showing versions

It looks like garbled output… I didn't use shell-escape, because the other
characters that are special for the shell that are used in versions should
not be escaped.

src/analyze/analyze-compare-versions.c

@@ -16,9 +16,9 @@ int verb_compare_versions(int argc, char *argv[], void *userdata) {
         if (argc == 3) {
                 r = strverscmp_improved(ASSERT_PTR(argv[1]), ASSERT_PTR(argv[2]));
                 printf("%s %s %s\n",
-                       argv[1],
+                       isempty(argv[1]) ? "''" : argv[1],
                        r < 0 ? "<" : r > 0 ? ">" : "==",
-                       argv[2]);
+                       isempty(argv[2]) ? "''" : argv[2]);
 
                 /* This matches the exit convention used by rpmdev-vercmp.
                  * We don't use named values because 11 and 12 don't have names. */