`nim sometask main.nonexistant` works even if main.nonexistant doesn't exist

[timotheecour]

Example

main.nims:

task foo, "some foo":
  echo "in task foo"

nim foo main.nims # case 1
nim foo main.nonexistant # case2
nim foo main # case3

ditto with things like help

Current Output

these all work and run the foo task

Expected Output

only case1 should work
case2 is a clear bug, since main.nonexistant doesn't exist
case3 is IMO a bug, IMO this shouldn't be legal, it's too loose (given that task foo is unconstrained and, after #17596, the extension is unconstrained too, including no extension)

Additional Information

• 1.5.1 8ee0eda