https://github.com/cyrusimap/cyrus-imapd/issues/2850

filled Argv[0] by '\0' instead of ' ' by default
used memset() instead of loop (better optimized by the compiler)

diff --git a/imap/setproctitle.c b/imap/setproctitle.c
index 4eb2b3139..3f5fb4614 100644
--- a/imap/setproctitle.c
+++ b/imap/setproctitle.c
@@ -196,7 +196,7 @@ typedef unsigned int    *pt_entry_t;
 # endif
 
 # ifndef SPT_PADCHAR
-#  define SPT_PADCHAR   ' '
+#  define SPT_PADCHAR   '\0'
 # endif
 
 # ifndef SPT_BUFSIZE
@@ -278,10 +278,9 @@ setproctitle(const char *fmt __attribute__((__unused__)), ...)
                 i = LastArgv - Argv[0] - 2;
                 buf[i] = '\0';
         }
+        memset(Argv[0], SPT_PADCHAR, LastArgv - Argv[0]);
         (void) strcpy(Argv[0], buf);
-        p = &Argv[0][i];
-        while (p < LastArgv)
-                *p++ = SPT_PADCHAR;
+
         Argv[1] = NULL;
 #  endif
 # endif /* SPT_TYPE != SPT_NONE */