render.c: reset last_breakable after cr.

Fixes jgm/pandoc#5033.

Author: jgm

src/render.c

@@ -45,6 +45,7 @@ static void S_out(cmark_renderer *renderer, const char *source, bool wrap,
       }
     }
     renderer->column = 0;
+    renderer->last_breakable = 0;
     renderer->begin_line = true;
     renderer->begin_content = true;
     renderer->need_cr -= 1;