Return success from IsaacReadFilePath after a valid read

[sylvesterkaczmarek]

Description

Make IsaacReadFilePath.compute() return True after successfully reading a file.

The node explicitly returns False for an empty or missing path, but the successful branch currently populates outputs:fileContents and then falls off the end of the function, implicitly returning None.

Python OmniGraph compute implementations in this extension use a boolean result to report compute success. Returning None on the only successful path makes the node's status inconsistent with both its error paths and neighbouring nodes.

Add the missing return True after a successful read and clarify the return-value docstring.

Validation

• regression test reads a temporary UTF-8 file through the node implementation
• verifies the file contents are populated
• verifies the compute result is True
• missing/empty-path behavior remains unchanged