std.cfg: Improved testing of std::system()

cfg/std.cfg

@@ -6185,6 +6185,7 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1" direction="in">
+      <!-- If a null pointer is given, command processor is checked for existence -->
       <not-uninit/>
     </arg>
   </function>

test/cfg/std.c

@@ -4356,6 +4356,13 @@ void uninitvar_system(void)
     (void)system(c);
 }
 
+void nullPointer_system(char *c)
+{
+    // If a null pointer is given, command processor is checked for existence
+    (void)system(NULL);
+    (void)system(c);
+}
+
 void uninitvar_zonetime(void)
 {
     time_t *tp;

test/cfg/std.cpp

@@ -3660,6 +3660,13 @@ void uninitvar_system(void)
     (void)std::system(c);
 }
 
+void nullPointer_system(char *c)
+{
+    // If a null pointer is given, command processor is checked for existence
+    (void)std::system(NULL);
+    (void)std::system(c);
+}
+
 void uninitvar_setw(void)
 {
     int i;