fix: dmesg_grep: avoid sigpipe on some systems (#519)

built from commit cc159fe7fd
 dated 2026-06-08 21:41:08 +0200
 by Stéphane Lesimple (speed47_github@speed47.net)

 Use 'grep -m 1' (works under Linux, busybox, BSD) instead of piping to head -n1

spectre-meltdown-checker.sh

@@ -13,7 +13,7 @@
 #
 # Stephane Lesimple
 #
-VERSION='26.36.0606627'
+VERSION='26.36.0608820'
 
 # --- Common paths and basedirs ---
 readonly VULN_SYSFS_BASE="/sys/devices/system/cpu/vulnerabilities"
@@ -3535,7 +3535,7 @@ dmesg_grep() {
         # dmesg truncated
         return 2
     fi
-    ret_dmesg_grep_grepped=$(dmesg 2>/dev/null | grep -E "$1" | head -n1)
+    ret_dmesg_grep_grepped=$(dmesg 2>/dev/null | grep -m 1 -E "$1")
     # not found:
     [ -z "$ret_dmesg_grep_grepped" ] && return 1
     # found, output is in $ret_dmesg_grep_grepped