Git: Use internal log highlighter for old git versions

Git didn't have RGB color support before version 2.3.0.
If an older version is used, fall back to the internal
log highlighter, i.e. don't disable it.

Amends commit d1b096699

Change-Id: I66f84dc4e79f7374d02f6d76c6f912c43e7f04bd
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitclient.cpp

@@ -557,6 +557,12 @@ public:
     }
 };
 
+static bool gitHasRgbColors()
+{
+    const unsigned gitVersion = GitClient::instance()->gitVersion();
+    return gitVersion >= 0x020300U;
+}
+
 class GitLogArgumentsWidget : public BaseGitLogArgumentsWidget
 {
     Q_OBJECT
@@ -608,8 +614,7 @@ public:
 
         QStringList graphArgs = {graphOption, "--oneline", "--topo-order"};
 
-        const unsigned gitVersion = GitClient::instance()->gitVersion();
-        if (gitVersion >= 0x020300U)
+        if (gitHasRgbColors())
             graphArgs << formatArg;
         else
             graphArgs << "--pretty=format:%h %d %an %s %ci";
@@ -1035,8 +1040,7 @@ void GitClient::status(const QString &workingDirectory) const
 
 static QStringList normalLogArguments()
 {
-    const unsigned gitVersion = GitClient::instance()->gitVersion();
-    if (gitVersion < 0x020300U)
+    if (!gitHasRgbColors())
         return {};
 
     auto colorName = [](Theme::Color color) { return creatorTheme()->color(color).name(); };
@@ -1095,7 +1099,7 @@ void GitClient::log(const QString &workingDirectory, const QString &fileName,
     if (arguments.contains(patchOption)) {
         arguments.removeAll(colorOption);
         editor->setHighlightingEnabled(true);
-    } else {
+    } else if (gitHasRgbColors()) {
         editor->setHighlightingEnabled(false);
     }
     if (!arguments.contains(graphOption) && !arguments.contains(patchOption))