Return success when get_total_system_memory() succeeds.

Fixes bug 11805; bugfix on 0.2.5.4-alpha.

changes/bug11805

+  o Minor bugfixes:
+    - Correctly detect the total available system memory. We tried to do this
+      in 0.2.5.4-alpha, but the code was set up to always return an error
+      value, even on success.
+      Fixes bug 11805; bugfix on 0.2.5.4-alpha. 

src/common/compat.c

@@ -3453,6 +3453,6 @@ get_total_system_memory(size_t *mem_out)
 
   *mem_out = mem_cached = (size_t) m;
 
-  return -1;
+  return 0;
 }