Fix excessive warnings by MSVC 2013 64bit about size_t->int truncation

C4267: 'initializing' : conversion from 'size_t' to 'int', possible loss of data

Change-Id: I91979c685bbbd84359f7f4e19911a21a408f5d23
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/debugger/debuggerengine.cpp

@@ -1859,7 +1859,7 @@ void DebuggerEngine::validateExecutable(DebuggerStartParameters *sp)
                     if (found)
                         break;
 
-                    const int len = strlen(str);
+                    const int len = int(strlen(str));
                     if (len == 0)
                         break;
                     str += len + 1;