[bin] meshroom_batch: Fix input parsing for Windows

[cbentejac]

Description

This PR fixes an issue that occurred when executing meshroom_batch on Windows. To determine the relationships between the provided input paths and the initialisation nodes, the strings given for the -i argument is parsed based on ":", which is the expected separator between the node instance and the input path(s).

On Linux, this works flawlessly since no path can contain a ":". On Windows however, ":" is a basic character in paths, which led to issues: since the input path was unexpectedly split, it was not correctly recognised, and the CameraInit node was never set with that input path. As a consequence, the process was stopping with a Nothing to compute for node CameraInit_1. error.

To prevent this, we now check that the first element after the split of the provided argument corresponds to a valid node name: this allows to distinguish an input such as CameraInit_1:/path/to/images from C:/path/to/images.