bitmap: Fix a crash with underspecified dimensions

From the reporter on #xorg-devel:

-!- thrig [thrig@unaffilaited/thrig] has joined #xorg-devel
<thrig> where does the code for bitmap live? there's a crash (or who
        knows on some platforms) if you `bitmap -size 42`

1 files changed, 6 insertions, 4 deletions

diff --git a/Bitmap.c b/Bitmap.c
index e168876..d074058 100644
--- a/Bitmap.c
+++ b/Bitmap.c
@@ -963,12 +963,14 @@ BWParseSize(String size, Dimension *width, Dimension *height)
 
   status = XParseGeometry(size, &x, &y, &w, &h);
 
-  if (status & (WidthValue | HeightValue)) {
+  if (status & WidthValue) {
     *width = (Dimension) w;
-    *height = (Dimension) h;
-    return True;
+    if (status & HeightValue) {
+      *height = (Dimension) h;
+      return True;
+    }
   }
-  else return False;
+  return False;
 
 }