[macros] Avoid excess vertical space for Annex C macros.

Author: jensmaurer

source/macros.tex

@@ -407,7 +407,7 @@
 
 %% Change descriptions
 \newcommand{\diffhead}[1]{\textbf{#1:}\space}
-\newcommand{\diffdef}[1]{\hfill\break\diffhead{#1}}
+\newcommand{\diffdef}[1]{\ifvmode\else\hfill\break\fi\diffhead{#1}}
 \ExplSyntaxOn
 \NewDocumentCommand \diffref { m } {
   \clist_set:Nx \l_tmpa_clist { #1 }