Avoid calling Copy from operator= if we are just resetting the nsXPIDLString. So now it is safe to reset an nsXPIDLCString or nsXPIDLString by setting it to null. r=waterson,a=jevering

string/obsolete/nsXPIDLString.cpp

@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;

xpcom/ds/nsXPIDLString.cpp

@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;

xpcom/string/obsolete/nsXPIDLString.cpp

@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;