Fix renaming substitution w/o value with <L:0>

There is not much point in adding the <L:0> parameter to a substitution vithout values,
but it is a valid setting so ...

Author: drdv

makefile-doc.awk

@@ -526,6 +526,10 @@ function display_substitutions(anchor, len_anchors, #locals
                    M || (!M && k == n) ? "\n" : "")
     printf(colorize_description_backticks(apply_output_specific_formatting(text)))
   }
+
+  if (!SUB_PARAMS_CURRENT["L"] && n == 0) {
+    printf("\n")
+  }
 }
 
 function display_anchor_with_data(anchor, description, section, len_anchors, #locals

test/integration/test-substitution-L0

@@ -0,0 +1,6 @@
+-v SUB='<L:0>$(TARGET):renamed:' -v VARS=0 test/Makefile.substitutions
+-----------------------
+Available targets:
+-----------------------
+renamed   Some target:
+-----------------------