fix manual_filter false positive

do explicit checks for the other branch being None

tests/ui/manual_filter.fixed

@@ -116,4 +116,31 @@ fn main() {
         },
         None => None,
     };
+
+    match Some(20) {
+        // Don't Lint, because `Some(3*x)` is not `None`
+        None => None,
+        Some(x) => {
+            if x > 0 {
+                Some(3 * x)
+            } else {
+                Some(x)
+            }
+        },
+    };
+
+    // Don't lint: https://github.com/rust-lang/rust-clippy/issues/10088
+    let result = if let Some(a) = maybe_some() {
+        if let Some(b) = maybe_some() {
+            Some(a + b)
+        } else {
+            Some(a)
+        }
+    } else {
+        None
+    };
+}
+
+fn maybe_some() -> Option<u32> {
+    Some(0)
 }

tests/ui/manual_filter.rs

@@ -240,4 +240,31 @@ fn main() {
         },
         None => None,
     };
+
+    match Some(20) {
+        // Don't Lint, because `Some(3*x)` is not `None`
+        None => None,
+        Some(x) => {
+            if x > 0 {
+                Some(3 * x)
+            } else {
+                Some(x)
+            }
+        },
+    };
+
+    // Don't lint: https://github.com/rust-lang/rust-clippy/issues/10088
+    let result = if let Some(a) = maybe_some() {
+        if let Some(b) = maybe_some() {
+            Some(a + b)
+        } else {
+            Some(a)
+        }
+    } else {
+        None
+    };
+}
+
+fn maybe_some() -> Option<u32> {
+    Some(0)
 }