PVS fixes

* build(PVS): exclude mpack and klib as they are external dependencies

* build(PVS): suppress warning V601

See https://pvs-studio.com/en/docs/warnings/v601/

* fix(PVS/V009): add top-level message

* fix(PVS/V547): expression 'p != NULL' is always true

* fix(PVS/V547): expression '* termpp == NULL' is always false

src/nvim/base64.c

@@ -1,3 +1,6 @@
+// This is an open source non-commercial project. Dear PVS-Studio, please check
+// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+
 #include <assert.h>
 #include <stddef.h>
 #include <string.h>

src/nvim/cmdexpand.c

@@ -169,10 +169,8 @@ static void wildescape(expand_T *xp, const char *str, int numfiles, char **files
       } else if (xp->xp_backslash & XP_BS_COMMA) {
         if (vim_strchr(files[i], ',') != NULL) {
           p = vim_strsave_escaped(files[i], ",");
-          if (p != NULL) {
-            xfree(files[i]);
-            files[i] = p;
-          }
+          xfree(files[i]);
+          files[i] = p;
         }
       }
 #ifdef BACKSLASH_IN_FILENAME

src/nvim/terminal.c

@@ -259,7 +259,7 @@ void terminal_open(Terminal **termpp, buf_T *buf, TerminalOptions opts)
 
   aucmd_restbuf(&aco);
 
-  if (*termpp == NULL) {
+  if (*termpp == NULL) {  // -V547
     return;  // Terminal has already been destroyed.
   }