Fix crash on break on invalid filename

breakpoints.cpp

@@ -229,11 +229,12 @@ BreakpointManager::ParseBreakpointLine(const std::string& input, std::string* fi
     std::string partial_filename = input.substr(0, sep_offs);
     // the user may have given a partial filename (e.g. without a path), so
     // walk through all files to find a match
-    *filename = debugger_->FindFileByPartialName(partial_filename);
-    if ((*filename).empty()) {
+    const char* found_filename = debugger_->FindFileByPartialName(partial_filename);
+    if (!found_filename) {
       std::cout << "Invalid filename.\n";
       return "";
     }
+    *filename = found_filename;
     return input.substr(sep_offs + 1);
   }
   return input;

debugger.cpp

@@ -345,7 +345,7 @@ Debugger::DumpStack()
   context_->DestroyFrameIterator(frames);
 }
 
-std::string
+const char*
 Debugger::FindFileByPartialName(const std::string partialname)
 {
   // the user may have given a partial filename (e.g. without a path), so

debugger.h

@@ -132,7 +132,7 @@ class Debugger {
 
   void DumpStack();
   void PrintCurrentPosition();
-  std::string FindFileByPartialName(const std::string partialname);
+  const char* FindFileByPartialName(const std::string partialname);
 
 private:
   std::shared_ptr<DebuggerCommand> ResolveCommandString(const std::string command);