Avoid implicit conversion to bool and actually use return value

The function was declared to return a bool (that was never read) and did so from
a function call returning an int. Make conversion explicit and actually test on
that return value.

Author: tautschnig

src/goto-programs/osx_fat_reader.cpp

@@ -88,5 +88,7 @@ bool osx_fat_readert::extract_gb(
 {
   PRECONDITION(has_gb_arch);
 
-  return run("lipo", {"lipo", "-thin", "hppa7100LC", "-output", dest, source});
+  return run(
+           "lipo", {"lipo", "-thin", "hppa7100LC", "-output", dest, source}) !=
+         0;
 }

src/goto-programs/read_goto_binary.cpp

@@ -135,7 +135,11 @@ bool read_goto_binary(
     if(osx_fat_reader.has_gb())
     {
       temporary_filet tempname("tmp.goto-binary", ".gb");
-      osx_fat_reader.extract_gb(filename, tempname());
+      if(osx_fat_reader.extract_gb(filename, tempname()))
+      {
+        message.error() << "failed to extract goto binary" << messaget::eom;
+        return true;
+      }
 
       std::ifstream temp_in(tempname(), std::ios::binary);
       if(!temp_in)