Show help text when ran in headless environment without args

[PaintNinja]

Currently the installer crashes if you run it without args in a headless environment. This PR makes it show the help text instead, which is more user-friendly. Also fixed a typo.

[LexManos]

Last time we tried this it didn't throw the headless exception and there wasn't a good non wrrorong way to detect it was headless. But if this works go for it.

[PaintNinja]

I found out about the headless exception from a log a user provided in the Discord:

JVM info: Oracle Corporation - 22.0.1 - 22.0.1+8-16
java.net.preferIPv4Stack=true
Current Time: 30/05/2024 22:18:59
Host: files.minecraftforge.net [104.21.58.163, 172.67.161.211]
Host: maven.minecraftforge.net [172.67.161.211, 104.21.58.163]
Host: libraries.minecraft.net [13.107.246.42]
Host: launchermeta.mojang.com [13.107.246.42]
Host: piston-meta.mojang.com [13.107.246.42]
Host: sessionserver.mojang.com [13.107.246.42]
Host: authserver.mojang.com [Unknown]
Data kindly mirrored by CreeperHost at https://www.creeperhost.net/
java.awt.HeadlessException:
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,
        at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
        at java.desktop/java.awt.Window.init(Window.java:501)
        at java.desktop/java.awt.Window.<init>(Window.java:453)
        at java.desktop/java.awt.Window.<init>(Window.java:608)
        at java.desktop/java.awt.Dialog.<init>(Dialog.java:674)
        at java.desktop/java.awt.Dialog.<init>(Dialog.java:519)
        at java.desktop/javax.swing.JDialog.<init>(JDialog.java:426)
        at java.desktop/javax.swing.JOptionPane.createDialog(JOptionPane.java:957)
        at net.minecraftforge.installer.InstallerPanel.run(InstallerPanel.java:258)
        at net.minecraftforge.installer.SimpleInstaller.launchGui(SimpleInstaller.java:182)
        at net.minecraftforge.installer.SimpleInstaller.main(SimpleInstaller.java:154)
Exception in thread "main"
java.awt.HeadlessException:
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,
        at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
        at java.desktop/java.awt.Window.<init>(Window.java:553)
        at java.desktop/java.awt.Frame.<init>(Frame.java:428)
        at java.desktop/java.awt.Frame.<init>(Frame.java:393)
        at java.desktop/javax.swing.SwingUtilities$SharedOwnerFrame.<init>(SwingUtilities.java:1925)
        at java.desktop/javax.swing.SwingUtilities.getSharedOwnerFrame(SwingUtilities.java:2001)
        at java.desktop/javax.swing.JOptionPane.getRootFrame(JOptionPane.java:1696)
        at java.desktop/javax.swing.JOptionPane.showOptionDialog(JOptionPane.java:875)
        at java.desktop/javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:677)
        at java.desktop/javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:648)
        at net.minecraftforge.installer.SimpleInstaller.launchGui(SimpleInstaller.java:185)
        at net.minecraftforge.installer.SimpleInstaller.main(SimpleInstaller.java:154)

So maybe they fixed it not throwing or it only throws sometimes? Dunno ¯\_ (ツ)_/¯

[LexManos]

Maybe, java does a lot of changes. As long as this doesn't bump the required java (it shouldn't iirc that exception is from java 1.4) then I'm fine with it.