LaTeX writer: ensure that unlabelled tables don't increment counter.

Closes #11141.

test/command/7272.md

@@ -14,6 +14,7 @@
   </tbody>
 </table>
 ^D
+{\def\LTcaptype{} % do not increment counter
 \begin{longtable}[]{@{}
   >{\raggedright\arraybackslash}p{(\linewidth - 0\tabcolsep) * \real{1.0000}}@{}}
 \toprule\noalign{}
@@ -25,4 +26,5 @@
 text2 }\strut
 \end{minipage} \\
 \end{longtable}
+}
 ```

test/command/8638.md

@@ -7,6 +7,7 @@
 | oranges | 4.25  |
 ^D
 \begin{frame}
+{\def\LTcaptype{} % do not increment counter
 \begin{longtable}[]{@{}lr@{}}
 \toprule\noalign{}
 fruit & price \\
@@ -16,5 +17,6 @@ apple & 2.05 \\
 oranges & 4.25 \\
 \bottomrule\noalign{}
 \end{longtable}
+}
 \end{frame}
 ```

test/command/9350.md

@@ -2,6 +2,7 @@
 % pandoc -f html -t latex
 <table><tbody><tr></tr></tbody></table>
 ^D
+{\def\LTcaptype{} % do not increment counter
 \begin{longtable}[]{@{}l@{}}
 \toprule\noalign{}
 \endhead
@@ -9,4 +10,5 @@
 \endlastfoot
  \\
 \end{longtable}
+}
 ```