Exception edges should not count when determining exit nodes

[tmr232]

Changes the criteria for exit nodes to either
have outdegree==0, or only have exception edges.

Closes #175.

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the bun lint on the code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• For visual changes, I've added screenshots to the PR.
• I accept that @tmr232 may be pedantic in the code review.

Description

Exit nodes are now rendered correctly inside try blocks.

Example for the following code:

def lookup_type(name):
	try:
		return gdb.lookup_type(name)
	except gdb.error:
		pass
	try:
		return gdb.lookup_type('struct ' + name)
	except gdb.error:
		pass
	try:
		return gdb.lookup_type('struct ' + name[1:]).pointer()
	except gdb.error:
		pass

Before	After