The `ed_screen_context()` function is approximately 700 lines long, and its main structure is a huge chain of `else if` statements. Some of the bodies did not return, but rather fell through and relied on the `return -1;` at the bottom of the function. This means that in order to truly understand what is going on in one of those `else if` blocks, it could be required to scroll past all the following `else if` blocks, double-checking that they all had an `else`, and then see what happens below. By adding explicit `return -1;` everywhere this happened, this is all avoided, increasing local understandability of the code. Furthermore, it makes the upcoming cleanup with the Clang-Tidy rule `readability-else-after-return` a lot easier to do. No functional changes.