qpkg/prereq.c (prereq): removed confused false error avoidance

The original idea was to just copy "stack" (now called "installed") to
"best" when done. In this case, "best" would remain NULL if "install"
had no entries, which would then be interpreted as a failure to resolve
the prerequisites.

However, since we allocate a new list for "best" anyway, this concern
no longer exists, and we can also get rid of the contorted mechanism
that was designed to work around this problem. (It was never put into
action because I wanted to make a regression test for it first.)

- prereq.c (prereq): removed commented-out and nonsensical avoidance of
  false error
- test/prereq: added test case with no prerequisite

qpkg/prereq.c

@@ -227,13 +227,6 @@ struct pkg **prereq(struct pkg *pkg)
 		.next = NULL
 	};
 
-#if 0
-	/* make sure we don't return NULL if all dependencies are met */
-	if (!installs) {
-		installs = alloc_type(struct pkg *);
-		install_max = 1;
-	}
-#endif
 	/* @@@ make list of pre-existing conflicts */
 	resolve(&deps, NULL, NULL);
 	free(installs);

qpkg/test/prereq

@@ -3,6 +3,17 @@
 
 ###############################################################################
 
+qpkg "no prereq for new package" prereq foo <<EOF
+Package: foo
+Version: 0
+Architecture: test
+Filename: foo_0_test.ipkg
+EOF
+expect <<EOF
+EOF
+
+###############################################################################
+
 qpkg "new prereq for new package" prereq foo <<EOF
 Package: bar
 Version: 1