[Processing] Fix setting of "multiline" setting for ParameterString

Author: radosuav

python/plugins/processing/core/parameters.py

@@ -572,7 +572,7 @@ def __init__(self, name='', description='', default='', multiline=False,
         Parameter.__init__(self, name, description)
         self.default = default
         self.value = None
-        self.multiline = multiline
+        self.multiline = parseBool(multiline)
         self.optional = parseBool(optional)
 
     def setValue(self, obj):