cmd-build-with-buildah: clean up overrides repo metadata

If there are no rpms then let's clean up the repo metadata if
it exists which should prevent cosmetic warts like:

```
Updating and loading repositories:
 overrides                              ???% |   0.0   B/s |  -1.0   B |  ?
>>> Curl error (37): Could not read a file:// file for file:///run/src/overrides
>>> Usable URL not found
```

Or fatal ones like:

```
error: Installing packages: importing RPMs: failed to open /run/src/overrides/rpm/systemd-258~rc3-2.fc44.x86_64.rpm
```

Author: dustymabe

src/cmd-build-with-buildah

@@ -162,8 +162,13 @@ build_with_buildah() {
     fi
 
     if [ -d overrides ]; then
-        if [[ -n $(ls overrides/rpm/*.rpm 2> /dev/null) ]]; then
-            (cd overrides/rpm && rm -rf .repodata && createrepo_c .)
+        if [ -d overrides/rpm ]; then
+            # Clean up any previous repo metadata
+            rm -rf overrides/rpm/repodata
+            if [[ -n $(ls overrides/rpm/*.rpm 2> /dev/null) ]]; then
+                # Generate new repo metadata since there are RPMs
+                (cd overrides/rpm && createrepo_c .)
+            fi
         fi
         set -- "$@" -v "$(realpath overrides)":/run/src/overrides
     fi