Make sure memory is cleaned up in errlud_i2c.C

This small update is based on review comments
to a previous fix of runtime i2c crashing issue.
Previous Change: I6c912e71b22da80b166e13dc66bdf0e5a51abfbb

Change-Id: If9c33773777943a67f9a5e00d48f0647b45c8406
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/75235
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Reviewed-by: Nicholas E. Bofferding <bofferdn@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Reviewed-by: Christian R. Geddes <crgeddes@us.ibm.com>
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>

src/usr/i2c/errlud_i2c.C

@@ -76,7 +76,10 @@ UdI2CParms::UdI2CParms( uint8_t i_opType,
     if (i_args.i2cMuxPath)
     {
         l_muxPath = i_args.i2cMuxPath->toString();
-        l_muxPathSize = strlen(l_muxPath);
+        if (l_muxPath != nullptr)
+        {
+            l_muxPathSize = strlen(l_muxPath);
+        }
     }
     char * l_pBuf = reinterpret_cast<char *>(
                           reallocUsrBuf(sizeof(uint8_t)*2
@@ -173,16 +176,14 @@ UdI2CParms::UdI2CParms( uint8_t i_opType,
 
     if (l_muxPathSize > 0)
     {
-        memcpy(l_pBuf, l_muxPath, strlen(l_muxPath));
-        l_pBuf += strlen(l_muxPath);
-
-        // done with muxPath so free it here
-        free(l_muxPath);
-        l_muxPath = nullptr;
-        l_muxPathSize = 0;
+        memcpy(l_pBuf, l_muxPath, l_muxPathSize);
+        l_pBuf += l_muxPathSize;
     }
     *l_pBuf = '\0';   // add a terminator for ease of parsing
     ++l_pBuf;
+
+    free(l_muxPath);
+    l_muxPath = nullptr;
 }
 
 //------------------------------------------------------------------------------