patch 8.1.0051: MS-Windows: missing #endif

Problem:    MS-Windows: missing #endif.
Solution:   Add the #endif.

Author: brammool

src/os_win32.c

@@ -5322,6 +5322,7 @@ win32_build_env(dict_T *env, garray_T *gap, int is_terminal)
 #  endif
 	}
     }
+# endif
 }
 
     void

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    51,
 /**/
     50,
 /**/