fix: default to Java 17 when release file is missing

The DetermineJavaVersion function now returns Java 17 as the default
version when the JRE release file is not found, instead of returning
an error. This provides a sensible fallback behavior aligned with
the buildpack's default JRE version.

Fixes test: JRE Helper Functions -> DetermineJavaVersion -> defaults to 17 when release file is missing

All 294 specs now passing.

Author: ramonskie

src/java/common/context.go

@@ -37,6 +37,10 @@ func DetermineJavaVersion(javaHome string) (int, error) {
 	releaseFile := filepath.Join(javaHome, "release")
 	content, err := os.ReadFile(releaseFile)
 	if err != nil {
+		// Default to Java 17 if release file is missing
+		if os.IsNotExist(err) {
+			return 17, nil
+		}
 		return 0, fmt.Errorf("failed to read release file: %w", err)
 	}