Fix copy&paste error in same_set

regression/goto-instrument/show-escape-analysis1/main.c

@@ -0,0 +1,13 @@
+#include <stdlib.h>
+
+void foo()
+{
+  int *leaked1=malloc(sizeof(int));
+  int *leaked2=malloc(sizeof(int));
+}
+
+int main()
+{
+  foo();
+  return 0;
+}

regression/goto-instrument/show-escape-analysis1/test.desc

@@ -0,0 +1,11 @@
+CORE
+main.c
+--show-escape-analysis
+^EXIT=0$
+^SIGNAL=0$
+^Aliases:.*(malloc.*leaked|leaked.*malloc)
+--
+^Aliases:.*(leaked1.*leaked2|leaked1.*leaked2)
+^warning: ignoring
+--
+leaked1 and leaked2 cannot alias

src/analyses/escape_analysis.cpp

@@ -305,16 +305,8 @@ bool escape_domaint::merge(
   locationt from,
   locationt to)
 {
-  if(b.has_values.is_false())
-    return false; // no change
-
-  if(has_values.is_false())
-  {
-    *this=b;
-    return true; // change
-  }
-
-  bool changed=false;
+  bool changed=has_values.is_false();
+  has_values=tvt::unknown();
 
   for(const auto &cleanup : b.cleanup_map)
   {

src/util/union_find.h

@@ -169,7 +169,7 @@ class union_find final
   bool same_set(const T &a, const T &b) const
   {
     const optionalt<number_type> na = numbers.get_number(a);
-    const optionalt<number_type> nb = numbers.get_number(a);
+    const optionalt<number_type> nb = numbers.get_number(b);
 
     if(na && nb)
       return uuf.same_set(*na, *nb);