MEDIUM: thread: Restric nbthread/thread-group(s) to very first global sections

nbhread, thead-group and thread-groups directives must only be defined in
very first global sections. It means no other section must have been parsed
before. Indeed, some parts of the configuratio depends on the value of these
settings and it is undefined to change them after.
diff --git a/src/thread.c b/src/thread.c
index 64ac476..59bfbf8 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -1312,6 +1312,11 @@
 	if (too_many_args(1, args, err, NULL))
 		return -1;
 
+	if (non_global_section_parsed == 1) {
+		memprintf(err, "'%s' not allowed if a non-global section was previously defined. This parameter must be declared in the first global section", args[0]);
+		return -1;
+	}
+
 	nbthread = strtol(args[1], &errptr, 10);
 	if (!*args[1] || *errptr) {
 		memprintf(err, "'%s' passed a missing or unparsable integer value in '%s'", args[0], args[1]);
@@ -1349,6 +1354,11 @@
 	long tnum, tend, tgroup;
 	int arg, tot;
 
+	if (non_global_section_parsed == 1) {
+		memprintf(err, "'%s' not allowed if a non-global section was previously defined. This parameter must be declared in the first global section", args[0]);
+		return -1;
+	}
+
 	tgroup = strtol(args[1], &errptr, 10);
 	if (!*args[1] || *errptr) {
 		memprintf(err, "'%s' passed a missing or unparsable integer value in '%s'", args[0], args[1]);
@@ -1445,6 +1455,11 @@
 
 	if (too_many_args(1, args, err, NULL))
 		return -1;
+
+	if (non_global_section_parsed == 1) {
+		memprintf(err, "'%s' not allowed if a non-global section was previously defined. This parameter must be declared in the first global section", args[0]);
+		return -1;
+	}
 
 	nbtgroups = strtol(args[1], &errptr, 10);
 	if (!*args[1] || *errptr) {