Fixed #4145: Formatter: Crash when double splats has restrictions in some cases

Author: Ary Borenszweig

spec/compiler/formatter/formatter_spec.cr

@@ -1015,4 +1015,6 @@ describe Crystal::Formatter do
   assert_format "def a\n  b(\n    1, # x\n    # y\n    2\n  )\nend"
   assert_format "def a\n  b(\n    a: 1, # x\n    # y\n    b: 2\n  )\nend"
   assert_format "def a\n  b(\n    1, # x\n    # y\n    a: 1, # x\n    # y\n    b: 2 # z\n  )\nend"
+
+  assert_format "def foo(a, **b : Int32)\nend"
 end

src/compiler/crystal/tools/formatter.cr

@@ -1477,10 +1477,8 @@ module Crystal
             comma_written = true
           end
           write_token :"**"
-          skip_space
-          check :IDENT
-          write double_splat
-          next_token_skip_space
+          double_splat.accept self
+          skip_space_or_newline
           if block_arg
             check :","
             write ","