Fix panic formatting processing instructions without attributes

internal/utils/utils.go

@@ -94,10 +94,16 @@ func FormatXml(reader io.Reader, writer io.Writer, indent string, colors int) er
 			_, _ = fmt.Fprintf(writer, "%s%s", tagColor("<?"), typedToken.Target)
 
 			pi := strings.TrimSpace(string(typedToken.Inst))
-			attrs := strings.Split(pi, " ")
-			for _, attr := range attrs {
-				attrComponents := strings.SplitN(attr, "=", 2)
-				_, _ = fmt.Fprintf(writer, " %s%s", attrComponents[0], attrColor("="+attrComponents[1]))
+			if pi != "" {
+				attrs := strings.Split(pi, " ")
+				for _, attr := range attrs {
+					attrComponents := strings.SplitN(attr, "=", 2)
+					if len(attrComponents) == 2 {
+						_, _ = fmt.Fprintf(writer, " %s%s", attrComponents[0], attrColor("="+attrComponents[1]))
+					} else {
+						_, _ = fmt.Fprintf(writer, " %s", attrComponents[0])
+					}
+				}
 			}
 
 			_, _ = fmt.Fprint(writer, tagColor("?>"), newline)

internal/utils/utils_test.go

@@ -39,6 +39,7 @@ func TestFormatXml(t *testing.T) {
 		"unformatted14.xml": "formatted14.xml",
 		"unformatted15.xml": "formatted15.xml",
 		"unformatted16.xml": "formatted16.xml",
+		"unformatted17.xml": "formatted17.xml",
 	}
 
 	for unformattedFile, expectedFile := range files {

test/data/xml/formatted17.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet?>
+<?xml-stylesheet type="text/xsl" href="style.xsl"?>
+<rss>
+  <channel>
+    <title>Test</title>
+  </channel>
+</rss>

test/data/xml/unformatted17.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet?>
+<?xml-stylesheet type="text/xsl" href="style.xsl"?>
+<rss><channel><title>Test</title></channel></rss>