Clear mutable inline style when it is empty.

Source/core/editing/RemoveCSSPropertyCommand.cpp

Index: Source/core/editing/RemoveCSSPropertyCommand.cpp
diff --git a/Source/core/editing/RemoveCSSPropertyCommand.cpp b/Source/core/editing/RemoveCSSPropertyCommand.cpp
index 6daa8410d93f0426dfa1a4951a6f3949d513f31c..f7d463aa3c244d638a464b406da16d997ca56acf 100644
--- a/Source/core/editing/RemoveCSSPropertyCommand.cpp
+++ b/Source/core/editing/RemoveCSSPropertyCommand.cpp
@@ -50,6 +50,9 @@ RemoveCSSPropertyCommand::~RemoveCSSPropertyCommand()
 void RemoveCSSPropertyCommand::doApply()
 {
     const StylePropertySet* style = m_element->inlineStyle();
+    if (!style)
+        return;
+
     m_oldValue = style->getPropertyValue(m_property);
     m_important = style->propertyIsImportant(m_property);