Fix pipe read return value

The function incorrectly returned false, whereas its return type is
ssize_t.

app/src/util/process_intr.c

@@ -5,7 +5,7 @@ sc_pipe_read_intr(struct sc_intr *intr, sc_pid pid, sc_pipe pipe, char *data,
                   size_t len) {
     if (intr && !sc_intr_set_process(intr, pid)) {
         // Already interrupted
-        return false;
+        return -1;
     }
 
     ssize_t ret = sc_pipe_read(pipe, data, len);
@@ -22,7 +22,7 @@ sc_pipe_read_all_intr(struct sc_intr *intr, sc_pid pid, sc_pipe pipe,
                       char *data, size_t len) {
     if (intr && !sc_intr_set_process(intr, pid)) {
         // Already interrupted
-        return false;
+        return -1;
     }
 
     ssize_t ret = sc_pipe_read_all(pipe, data, len);