BR3041451: Implement upper bound for %rep counter

Since %rep counter is a 64 bit signed integer we have to use some
"maximum possible value" limit (upper bound) otherwise there may be
a situation when %rep counter is 0 or even negative while user
has been passing big positive integer value.

Reported-by: nasm64developer
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
diff --git a/doc/changes.src b/doc/changes.src
index a7ee231..d015f9e 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -9,6 +9,9 @@
 
 \S{cl-2.09} Version 2.09
 
+\b Fixed assignment the magnitude of \c{%rep} counter. It is limited
+  to 62 bits now.
+
 \b Fixed NULL dereference if argument of \c{%strlen} resolves
   to whitespace. For example if nonexistent macro parameter is used.