Reject non-positive camera sizes early

Throw an exception on parsing if the camera size dimensions are not both
positive.

server/src/main/java/com/genymobile/scrcpy/Options.java

@@ -475,6 +475,9 @@ public class Options {
         }
         int width = Integer.parseInt(tokens[0]);
         int height = Integer.parseInt(tokens[1]);
+        if (width <= 0 || height <= 0) {
+            throw new IllegalArgumentException("Invalid non-positive size dimension: \"" + size + "\"");
+        }
         return new Size(width, height);
     }