Check if PURL is valid before adding it to queries (google#291)

This is also probably where having a verbosity level when reporting
could be useful. By default we probably would not want to print out
every invalid PURL, but this could be helpful if someone wants to find
what invalid PURLs they have in their SBOM.

pkg/osvscanner/osvscanner.go

@@ -237,7 +237,14 @@ func scanSBOMFile(r *output.Reporter, query *osv.BatchedQuery, path string) erro
 		defer file.Close()
 
 		count := 0
+		ignoredCount := 0
 		err = provider.GetPackages(file, func(id sbom.Identifier) error {
+			_, err := PURLToPackage(id.PURL)
+			if err != nil {
+				ignoredCount++
+				//nolint:nilerr
+				return nil
+			}
 			purlQuery := osv.MakePURLRequest(id.PURL)
 			purlQuery.Source = models.SourceInfo{
 				Path: path,
@@ -251,6 +258,10 @@ func scanSBOMFile(r *output.Reporter, query *osv.BatchedQuery, path string) erro
 		if err == nil {
 			// Found the right format.
 			r.PrintText(fmt.Sprintf("Scanned %s as %s SBOM and found %d packages\n", path, provider.Name(), count))
+			if ignoredCount > 0 {
+				r.PrintText(fmt.Sprintf("Ignored %d packages with invalid PURLs\n", ignoredCount))
+			}
+
 			return nil
 		}