Add a guard against an empty range in the EXT4 formatter

[dkovba]

Adds a guard against an empty range in the EXT4 formatter to prevent a possible crash:

Swift/arm64e-apple-macos.swiftinterface:6314: Fatal error: Range requires lowerBound <= upperBound

[wlan0]

I agree that this loop would need guarding if the lower bound could exceed the upper bound, but with the current math I can’t find a reachable state where that happens.

Can you add a failing regression test or share the exact formatter input that makes
usedGroupDescriptorBlocks + 1 > self.groupDescriptorBlocks ?

[dkovba]

@wlan0 Added a test reproducing the crash. However, to reproduce the crash, I had to remove reserved blocks in groupDescriptorBlocks:

-            ((groupCount - 1) / groupsPerDescriptorBlock + 1) * 32                                           
+            (groupCount - 1) / groupsPerDescriptorBlock + 1