fix: issuses detected by static analyzer (#4440)

* fix incorrect variable check

* remove duplicated check

* remove unneeded const cast

Author: cyyever

include/pybind11/attr.h

@@ -399,7 +399,7 @@ struct process_attribute<doc> : process_attribute_default<doc> {
 template <>
 struct process_attribute<const char *> : process_attribute_default<const char *> {
     static void init(const char *d, function_record *r) { r->doc = const_cast<char *>(d); }
-    static void init(const char *d, type_record *r) { r->doc = const_cast<char *>(d); }
+    static void init(const char *d, type_record *r) { r->doc = d; }
 };
 template <>
 struct process_attribute<char *> : process_attribute<const char *> {};

include/pybind11/eigen/tensor.h

@@ -176,7 +176,7 @@ struct type_caster<Type, typename eigen_tensor_helper<Type>::ValidType> {
                 return false;
             }
 
-            if (!convert && !temp.dtype().is(dtype::of<typename Type::Scalar>())) {
+            if (!temp.dtype().is(dtype::of<typename Type::Scalar>())) {
                 return false;
             }
         }

include/pybind11/pytypes.h

@@ -501,7 +501,7 @@ struct error_fetch_and_normalize {
                             "active exception.");
         }
         const char *exc_type_name_norm = detail::obj_class_name(m_type.ptr());
-        if (exc_type_name_orig == nullptr) {
+        if (exc_type_name_norm == nullptr) {
             pybind11_fail("Internal error: " + std::string(called)
                           + " failed to obtain the name "
                             "of the normalized active exception type.");