fix(bq_driver): stop empty dialog areas acting as a documentation link

Clicking a blank part of the DSN setup dialog or the Advanced Options dialog
could open a browser at the BigQuery ODBC/JDBC drivers page.

Both dialogs hit-test WM_LBUTTONDOWN against the documentation hyperlink's
rectangle, but the CreateHyperlinkLabel calls that would create that control
are currently commented out. GetDlgItem therefore returns NULL,
GetClientRect(NULL, &rect) fails and leaves 'rect' holding whatever was on
the stack, and PtInRect matches that uninitialised rectangle -- so clicks on
unrelated parts of the dialog launch the browser. Which clicks match varies
between runs, since it depends on stack contents.

Bail out when the control does not exist or its rectangle cannot be read, and
zero-initialise the rectangle so it can never hold garbage.

Author: Joshua McHenry

google/cloud/odbc/bq_driver/internal/driver_adv_opt_form.cc

@@ -639,12 +639,20 @@ LRESULT CALLBACK AdvanceOptions::AdvanceOptProc(HWND hwnd, UINT u_msg,
       return 1;  // Indicate we handled the background redraw
     }
     case WM_LBUTTONDOWN: {
+      // Same guard as in driver_form.cc: the documentation hyperlink is not
+      // created at present, so without checking for a NULL control the
+      // uninitialised rect can swallow clicks anywhere on the dialog.
+      HWND h_hyperlink = GetDlgItem(hwnd, kIdcHyperlink2);
+      if (h_hyperlink == NULL) {
+        break;
+      }
+      RECT rect = {};
+      if (!GetClientRect(h_hyperlink, &rect)) {
+        break;
+      }
       POINT pt;
       GetCursorPos(&pt);
       ScreenToClient(hwnd, &pt);
-      HWND h_hyperlink = GetDlgItem(hwnd, kIdcHyperlink2);
-      RECT rect;
-      GetClientRect(h_hyperlink, &rect);
       MapWindowPoints(h_hyperlink, hwnd, (LPPOINT)&rect, 2);
       if (PtInRect(&rect, pt)) {
         ShellExecute(NULL, "open", kBigQueryDocsURL, NULL, NULL, SW_SHOWNORMAL);

google/cloud/odbc/bq_driver/internal/driver_form.cc

@@ -908,12 +908,22 @@ LRESULT CALLBACK DriverForm::WindowProc(HWND hwnd, UINT u_msg, WPARAM w_param,
       return 1;  // Indicate we handled the background redraw
     }
     case WM_LBUTTONDOWN: {
+      // The documentation hyperlink is currently not created (see the
+      // commented-out CreateHyperlinkLabel call), so GetDlgItem returns NULL.
+      // Without these guards GetClientRect fails and leaves 'rect'
+      // uninitialised, and clicks on empty parts of the dialog can fall inside
+      // that garbage rectangle and launch a browser.
+      HWND h_hyperlink = GetDlgItem(hwnd, kIdcHyperlink3);
+      if (h_hyperlink == NULL) {
+        break;
+      }
+      RECT rect = {};
+      if (!GetClientRect(h_hyperlink, &rect)) {
+        break;
+      }
       POINT pt;
       GetCursorPos(&pt);
       ScreenToClient(hwnd, &pt);
-      HWND h_hyperlink = GetDlgItem(hwnd, kIdcHyperlink3);
-      RECT rect;
-      GetClientRect(h_hyperlink, &rect);
       MapWindowPoints(h_hyperlink, hwnd, (LPPOINT)&rect, 2);
       if (PtInRect(&rect, pt)) {
         ShellExecute(NULL, "open", kBigQueryDocsURL, NULL, NULL, SW_SHOWNORMAL);