lib/systems/inspect: partially apply hasPrefix

lib/systems/inspect.nix

@@ -27,6 +27,8 @@ let
     execFormats
     ;
 
+  hasArmv7Prefix = hasPrefix "armv7";
+
   # Based on lib.attrsets.matchAttrs, but with:
   # - the initial isAttrs assertion removed, since this function is only ever
   # called with attrsets
@@ -137,7 +139,7 @@ rec {
       {
         cpu = { inherit arch; };
       }
-    ) (filter (cpu: hasPrefix "armv7" cpu.arch or "") (attrValues cpuTypes));
+    ) (filter (cpu: cpu ? arch && hasArmv7Prefix cpu.arch) (attrValues cpuTypes));
     isAarch64 = {
       cpu = {
         family = "arm";