only create directory for stocks when necessary

This avoids printing an inacurate error every time.

inkycal/modules/inkycal_stocks.py

@@ -82,7 +82,8 @@ class Stocks(inkycal_module):
         tmpPath = '/tmp/inkycal_stocks/'
 
         try:
-            os.mkdir(tmpPath)
+            if not os.path.exists(tmpPath):
+                os.mkdir(tmpPath)
         except OSError:
             print(f"Creation of tmp directory {tmpPath} failed")
         else: