Import asc: Exclude nodata values for mesh creation - #1020

I tried to work on the following "#TODO" comment for the operator for importing asc-files.

            for x in range(0, ncols, step):
                # TODO: exclude nodata values (implications for face generation)
                if not (self.importMode == 'CLOUD' and coldata[x] == nodata):

In my case, nodata filtering didn’t work because nodata is declared as float, while coldata[x] was a str in my case, so the comparison returned False.
To address this, I restructured the logic so that nodata vertices are kept initially, and any faces referencing a nodata vertex are removed later in the process.
This approach worked for my ASC file, but it still needs more testing to confirm that it behaves correctly across different datasets.