bug: fixes bug with error out with using kompose convert with no -f (#1725)

#### What type of PR is this?

<!--
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/kind cleanup
/kind documentation
/kind feature
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/kind bug

Fixes a validation bug where if you do not provide a compose.yaml or
docker-compose.yaml it will nil point error out rather than have an
appropriate "file not found" output.

#### Which issue(s) this PR fixes:
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Usage: `Fixes #<issue number>`, or `Fixes (paste link of issue)`.
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Closes https://github.com/kubernetes/kompose/issues/1719

#### Special notes for your reviewer:

Signed-off-by: Charlie Drage <charlie@charliedrage.com>

pkg/app/app.go

@@ -146,18 +146,18 @@ func ValidateFlags(args []string, cmd *cobra.Command, opt *kobject.ConvertOption
 // ValidateComposeFile validates the compose file provided for conversion
 func ValidateComposeFile(opt *kobject.ConvertOptions) error {
 	if len(opt.InputFiles) == 0 {
+		// Go through a range of "default" file names to see if tany ofthem exist in the current directory
 		for _, name := range DefaultComposeFiles {
 			_, err := os.Stat(name)
 			if err != nil {
 				log.Debugf("'%s' not found: %v", name, err)
-				return err
 			} else {
 				opt.InputFiles = []string{name}
 				return nil
 			}
 		}
-
-		log.Fatal("No 'docker-compose' file found")
+		// Return an error message that no compose or docker-compose yaml files were found
+		return fmt.Errorf("No compose or docker-compose yaml file found in the current directory")
 	}
 	return nil
 }