rivertile: properly validate -main-ratio flag

 rivertile/main.zig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/rivertile/main.zig b/rivertile/main.zig
index dbf90c6..3c88843 100644
--- a/rivertile/main.zig
+++ b/rivertile/main.zig
@@ -348,8 +348,12 @@ pub fn main() !void {
             fatalPrintUsage("invalid value '{s}' provided to -main-count", .{raw});
     }
     if (result.argFlag("-main-ratio")) |raw| {
-        default_main_ratio = fmt.parseFloat(f64, raw) catch
+        default_main_ratio = fmt.parseFloat(f64, raw) catch {
             fatalPrintUsage("invalid value '{s}' provided to -main-ratio", .{raw});
+        };
+        if (default_main_ratio < 0.1 or default_main_ratio > 0.9) {
+            fatalPrintUsage("invalid value '{s}' provided to -main-ratio", .{raw});
+        }
     }
 
     const display = wl.Display.connect(null) catch {