Adjusted the inject function code to be flat like the provide function (#481)

* Adjusted the inject function code to be flat like the provide function

* Update src/apis/inject.ts

Co-authored-by: Jacek Karczmarczyk <jkarczm@gmail.com>

Co-authored-by: Jacek Karczmarczyk <jkarczm@gmail.com>

Author: kahirokunn

src/apis/inject.ts

@@ -48,17 +48,19 @@ export function inject(
   }
 
   const vm = getCurrentInstance()
-  if (vm) {
-    const val = resolveInject(key, vm)
-    if (val !== NOT_FOUND) {
-      return val
-    } else {
-      if (defaultValue === undefined && __DEV__) {
-        warn(`Injection "${String(key)}" not found`, vm)
-      }
-      return defaultValue
-    }
-  } else {
+  if (!vm) {
     warn(`inject() can only be used inside setup() or functional components.`)
+    return
+  }
+
+  const val = resolveInject(key, vm)
+  if (val !== NOT_FOUND) {
+    return val;
   }
+  
+  if (defaultValue === undefined && __DEV__) {
+    warn(`Injection "${String(key)}" not found`, vm)
+  }
+
+  return defaultValue
 }