Don't "exit" android-configure, which is meant to be "source"d

[fdgonthier]

• Version: 12.18.4
• Platform: Linux

What steps will reproduce the bug?

Run android-configure, as prescribed, but without parameters

source ./android-configure

This will terminate my shell window.

What is the expected behavior?

Just show the error message and return.

Additional information

PR will soon follow.