[lldb][Module][NFC] Use early-return style in LoadScriptingResourceInTarget (#186392)
Planning on adding more to this function/loop soon. Making it
early-return style (as suggested by the LLVM style guide) makes those
changes easier to reason about.
Drive-by:
* Reduced the indentation of the loop by doing an early-continue if the
`FileSpec` is invalid or doesn't exist