[vm, profiler] Fix unsigned underflow with an empty set of profiler s…

…ymbols.

Bug: FL-261
Change-Id: I5eae25134816d24b91cda8afa86deb402c7d9b52
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105060
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/vm/native_symbol_fuchsia.cc

@@ -79,7 +79,7 @@ class NativeSymbols {
 
   NativeSymbols* next_;
   const char* const dso_name_;
-  uint32_t num_entries_;
+  intptr_t num_entries_;
   Entry* entries_;
   const char* name_table_;