wrappers: Take the argv null terminator into account when checking for overflows

When adding the terminator without incrementing arg and checking for
overflows with "arg > max_arg", we need to allocate space for one
extra element for the implicit terminator.

wrappers/clang-target-wrapper.c

@@ -272,7 +272,7 @@ int _tmain(int argc, TCHAR* argv[]) {
     }
 
     int max_arg = argc + 20;
-    const TCHAR **exec_argv = malloc(max_arg * sizeof(*exec_argv));
+    const TCHAR **exec_argv = malloc((max_arg + 1) * sizeof(*exec_argv));
     int arg = 0;
     if (getenv("CCACHE"))
         exec_argv[arg++] = _T("ccache");

wrappers/windres-wrapper.c

@@ -389,7 +389,7 @@ int _tmain(int argc, TCHAR* argv[]) {
 
 
     int max_arg = 2 * argc + 20;
-    const TCHAR **exec_argv = malloc(max_arg * sizeof(*exec_argv));
+    const TCHAR **exec_argv = malloc((max_arg + 1) * sizeof(*exec_argv));
     int arg = 0;
 
     if (!_tcscmp(input_format, _T("rc"))) {