Fix copy / move behaviour of Maps object.

Currently, moving or copying a Maps object leads to double free of MapInfo.

Even moving a Maps object  did not prevent this, as after a move
the object only has to be in an "unspecified but valid state", which can
be the original state for a vector of raw pointers (but not for a vector
of unique_ptrs).

Changing to unique_ptrs is the most failsafe way to make sure we never
accidentally destruct MapInfo.

Test: atest libuwindstack_test
      Failed LocalUnwinderTest#unwind_after_dlopen which also fails at master.

Change-Id: Id1c9739b334da5c1ba532fd55366e115940a66d3
diff --git a/libunwindstack/Global.cpp b/libunwindstack/Global.cpp
index fdfd705..a20be00 100644
--- a/libunwindstack/Global.cpp
+++ b/libunwindstack/Global.cpp
@@ -77,7 +77,7 @@
   //   f0000-f2000 0 r-- /system/lib/libc.so
   //   f2000-f3000 2000 rw- /system/lib/libc.so
   MapInfo* map_start = nullptr;
-  for (MapInfo* info : *maps) {
+  for (const auto& info : *maps) {
     if (map_start != nullptr) {
       if (map_start->name == info->name) {
         if (info->offset != 0 &&
@@ -96,7 +96,7 @@
     }
     if (map_start == nullptr && (info->flags & PROT_READ) && info->offset == 0 &&
         !info->name.empty()) {
-      map_start = info;
+      map_start = info.get();
     }
   }
 }