[bin][extractlinedata] do not overwrite previous .csv files

When multiple vtk files were given as arguments to the script together
with a base name for the output .csv files, a single csv file was
created that contained the data of the last given vtk file. This commit
adds an index to the file names in case multiple vtk files are provided.

bin/postprocessing/extractlinedata.py

@@ -28,7 +28,7 @@ if not outDirectory == '' and not os.path.exists(outDirectory):
     os.makedirs(outDirectory)
 
 # loop over all vtk files
-counter = 1
+counter = 0
 for curFile in args['files']:
 
     # if no output directory was specified, use the directory of the given file
@@ -39,13 +39,15 @@ for curFile in args['files']:
     # if no basename was specified, reuse the file name for the .csv file
     if args['outFile'] == '':
         csvFileName = os.path.join(curOutDirectory, os.path.splitext(os.path.basename(curFile))[0] + ".csv")
+    elif len(args['files']) > 1:
+        csvFileName = os.path.join(curOutDirectory, args['outFile'] + "_" + str(counter) + ".csv")
     else:
         csvFileName = os.path.join(curOutDirectory, args['outFile'] + ".csv")
+    counter += 1
 
     # print progress to command line
     if args['verbosity'] == 1:
         print("Processing file ({}/{}): {}".format(counter, len(args['files']), os.path.basename(curFile)))
-    counter += 1
 
     # load vtk file
     if os.path.splitext(curFile)[1] == ".vtp":