Kernel: Unmapping a non-mapped region with munmap() should be a no-op

Not a regression per se from 0fcb9ef
since we were crashing before that which is obviously worse.

Author: awesomekling

Kernel/VM/Space.cpp

@@ -92,7 +92,7 @@ KResult Space::unmap_mmap_range(VirtualAddress addr, size_t size)
     // Try again while checking multiple regions at a time.
     auto const& regions = find_regions_intersecting(range_to_unmap);
     if (regions.is_empty())
-        return EINVAL;
+        return KSuccess;
 
     // Check if any of the regions is not mmap'ed, to not accidentally
     // error out with just half a region map left.

Tests/Kernel/TestMunMap.cpp

@@ -10,8 +10,7 @@
 
 TEST_CASE(munmap_zero_page)
 {
-    // munmap of the unmapped zero page should always fail.
+    // munmap of the unmapped zero page should always "succeed".
     auto res = munmap(0x0, 0xF);
-    EXPECT_EQ(res, -1);
-    EXPECT_EQ(errno, EINVAL);
+    EXPECT_EQ(res, 0);
 }