Ignore whitespace around comma-separated config values

'inputs=/a, /b' was read as '/a' and ' /b', so /b was skipped, and
excluded patterns with spaces around them never matched. Strip
whitespace from each value, and ignore empty exclude entries.

simple_backup/simple_backup.py

@@ -753,7 +753,7 @@ def _read_config(config_file, user: Optional[str] = None):
         section = 'default'
         inputs = config.get(section, 'inputs')
 
-    inputs = inputs.split(',')
+    inputs = [i.strip() for i in inputs.split(',')]
     inputs = _expand_inputs(inputs, user)
     inputs = list(set(inputs))
 
@@ -770,7 +770,7 @@ def _read_config(config_file, user: Optional[str] = None):
 
     try:
         exclude = config.get(section, 'exclude')
-        exclude = exclude.split(',')
+        exclude = [e.strip() for e in exclude.split(',') if e.strip() != '']
     except configparser.NoOptionError:
         exclude = []