rusticl/program: fix CL_PROGRAM_BINARIES for devs with no builds

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/10611
Fixes: e028baa177 ("rusticl/program: implement clCreateProgramWithBinary")
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27633>

src/gallium/frontends/rusticl/core/program.rs

@@ -517,7 +517,12 @@ impl Program {
         for (i, d) in self.devs.iter().enumerate() {
             let mut ptr = ptrs[i];
             let info = lock.dev_build(d);
-            let spirv = info.spirv.as_ref().unwrap().to_bin();
+
+            // no spirv means nothing to write
+            let Some(spirv) = info.spirv.as_ref() else {
+                continue;
+            };
+            let spirv = spirv.to_bin();
 
             unsafe {
                 // 1. binary format version