Fixed ineffectual assignments (#7555)

Don't assign values we never use.

models/git_diff.go

@@ -543,7 +543,7 @@ func ParsePatch(maxLines, maxLineCharacters, maxFiles int, reader io.Reader) (*D
 
 		// Get new file.
 		if strings.HasPrefix(line, cmdDiffHead) {
-			middle := -1
+			var middle int
 
 			// Note: In case file name is surrounded by double quotes (it happens only in git-shell).
 			// e.g. diff --git "a/xxx" "b/xxx"

routers/user/setting/security_twofa.go

@@ -81,7 +81,6 @@ func twofaGenerateSecretAndQr(ctx *context.Context) bool {
 	// Filter unsafe character ':' in issuer
 	issuer := strings.Replace(setting.AppName+" ("+setting.Domain+")", ":", "", -1)
 	if otpKey == nil {
-		err = nil // clear the error, in case the URL was invalid
 		otpKey, err = totp.Generate(totp.GenerateOpts{
 			SecretSize:  40,
 			Issuer:      issuer,