Fix VimwikiAddHeaderLevel map (like 3=), borken by previous 5e564bb10d, (Issue #1270)

autoload/vimwiki/base.vim

@@ -2236,7 +2236,7 @@ function! vimwiki#base#AddHeaderLevel(...) abort
   " Clause, argument must be <= 1
   " Actually argument is not used :-)
   if a:1 > 1
-    call vimwiki#base#AddHeaderLevel(1)
+    call vimwiki#base#AddHeaderLevel(a:1 - 1)
   endif
   let lnum = line('.')
   let line = getline(lnum)
@@ -2270,7 +2270,7 @@ function! vimwiki#base#RemoveHeaderLevel(...) abort
   " Clause, argument must be <= 1
   " Actually argument is not used :-)
   if a:1 > 1
-    call vimwiki#base#RemoveHeaderLevel(1)
+    call vimwiki#base#RemoveHeaderLevel(a:1 - 1)
   endif
   let lnum = line('.')
   let line = getline(lnum)

doc/vimwiki.txt

@@ -4011,6 +4011,11 @@ master is retained as a legacy mirror of the dev branch.
 
 This is somewhat experimental, and will probably be refined over time.
 
+Fixed:~
+    * Issue #1270: VimwikiAddHeaderLevel map (3=) was broken by a previous
+      refactoring commit
+
+
 2022.03.15~
 
 New:~

test/issue_1270_add_header_level.vader

@@ -0,0 +1,41 @@
+# Non regression tests for issue: #1270
+
+
+Given vimwiki (Dummy heading):
+  # Test
+
+Execute (Set syntax markdown):
+  call SetSyntax('markdown')
+
+Execute (call add header 1):
+  call vimwiki#base#AddHeaderLevel(1)
+
+Expect (Heading 2):
+  ## Test
+
+Execute (call add header 2):
+  call vimwiki#base#AddHeaderLevel(2)
+
+Expect (Heading 3):
+  ### Test
+
+Execute (call add header 5):
+  call vimwiki#base#AddHeaderLevel(5)
+
+Expect (Heading6):
+  ###### Test
+
+Do (5=):
+  5=
+
+Expect (Heading6):
+  ###### Test
+
+Given vimwiki (Dummy heading 6):
+  ###### Test
+
+Do (5-):
+  5-
+
+Expect (Heading decreased by 5):
+  # Test