Improve struct and pointer autocompletion in C (#4231)

* Add explicit trigger characters for C (#4226)

* Stop completion before issuing subsequent requests (#4226)

Co-authored-by: Marios Sioutis <26476573+s-marios@users.noreply.github.com>

rplugin/python3/deoplete/sources/ale.py

@@ -32,6 +32,7 @@ class Source(Base):
             'rust': r'(\.|::)\w*$',
             'typescript': r'(\.|\'|")\w*$',
             'cpp': r'(\.|::|->)\w*$',
+            'c': r'(\.|->)\w*$',
         }
 
     # Returns an integer for the start position, as with omnifunc.