Fix #425604 - Conditional jump or move depends on uninitialised value(s)

It occurs on first occurence of slave timeout (found with Valgrind 3.3.0).
Reported by Henrik Munktell.

NEWS

@@ -14,6 +14,11 @@ libmodbus 2.2.0 (2009-XX-01)
   Reported and tested by Yishin Li.
 - Fix #378981 - CRC error on RTU response doesn't return negative value
   Reported by Henrik Munktell.
+- Fix report slave ID request
+  Patch (bzr) provided by Paul Fertser .
+- Fix #425604 - Conditional jump or move depends on uninitialised value(s)
+  Occurs on first occurence of slave timeout.
+  Reported by Henrik Munktell.
 
 libmodbus 2.0.3 (2009-03-22)
 ============================
@@ -63,7 +68,7 @@ libmodbus 2.0.0 (2008-05-18)
 - Declare many static functions and const arrays
 - Enhance an integer division
 - The GNU licences LGPL and GPL are in version 3
-- Debian and RPM packages (#224496) 
+- Debian and RPM packages (#224496)
 - Many cleanups
 - Fix #159443 reported by Stefan Bisanz
   Index of incoming data in force multiple coils function

src/modbus.c

@@ -532,6 +532,10 @@ static int receive_msg(modbus_param_t *mb_param,
         enum { FUNCTION, BYTE, COMPLETE };
         int state;
 
+        /* Initialize the return length before a call to WAIT_DATA because a
+         * time out can quit the function. */
+        (*p_msg_length) = 0;
+
         if (mb_param->debug) {
                 if (msg_length_computed == MSG_LENGTH_UNDEFINED)
                         printf("Waiting for a message...\n");
@@ -566,10 +570,7 @@ static int receive_msg(modbus_param_t *mb_param,
         select_ret = 0;
         WAIT_DATA();
 
-        /* Initialize the readin the message */
-        (*p_msg_length) = 0;
         p_msg = msg;
-
         while (select_ret) {
                 if (mb_param->type_com == RTU)
                         read_ret = read(mb_param->fd, p_msg, length_to_read);