Ensure containers have a size of at least 1px after resize

Fixes #2226.
Fixes #2776.
Fixes #3241.
Related to #3194.

include/resize.h

@@ -25,6 +25,13 @@ void resize_graphical_handler(Con *first, Con *second, orientation_t orientation
  */
 bool resize_neighboring_cons(Con *first, Con *second, int px, int ppt);
 
+/**
+ * Calculate the minimum percent needed for the given container to be at least 1
+ * pixel.
+ *
+ */
+double percent_for_1px(Con *con);
+
 /**
  * Calculate the given container's new percent given a change in pixels.
  *