MM-54259 - Fix: Panic in isMobilePostGA (#505)

* remove isMobilePostGA code

* Revert "remove isMobilePostGA code"

This reverts commit 0ab4977.

* fix the crash

server/utils.go

@@ -113,7 +113,11 @@ func isMobilePostGA(r *http.Request) (mobile, postGA bool) {
 	//   https://mattermost.atlassian.net/browse/MM-48929
 	userAgent := r.Header.Get("User-Agent")
 	fields := strings.Fields(userAgent)
-	clientAgent := fields[0] // safe to assume there's at least one
+	if len(fields) == 0 {
+		return false, false
+	}
+
+	clientAgent := fields[0]
 	isMobile := strings.HasPrefix(clientAgent, "rnbeta") || strings.HasPrefix(clientAgent, "Mattermost")
 	if !isMobile {
 		return false, false

server/utils_test.go

@@ -47,6 +47,13 @@ func Test_isMobilePostGA(t *testing.T) {
 			wantMobile: true,
 			wantPostGA: true,
 		},
+		{
+			name:       "no user agent",
+			userAgent:  "",
+			params:     "",
+			wantMobile: false,
+			wantPostGA: false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {